Scattering of light by a large, densely packed agglomerate of small silica spheres.

We model the measured phase function and degree of linear polarization of a macroscopic agglomerate made of micrometer-scale silica spheres using the methodology of multiple scattering. In the laboratory work, the agglomerate is produced ballistically, characterized by scanning electron microscopy, and measured with the $ {\text{PROGRA}^{2}} $PROGRA2 instrument to obtain the light scattering properties. The model phase function and degree of polarization are in satisfactory agreement with the experimental data. To our best knowledge, this is the first time the degree of linear polarization has been modeled well for a large, densely packed agglomerate composed of small particles with known sizes and shapes. The study emphasizes the relevance of the degree of linear polarization and gives insights into the effects of particle aggregation on the scattering characteristics.

Scattering and absorption in dense discrete random media of irregular particles.

We present an approximate numerical solution for the multiple scattering problem involving densely packed arbitrarily shaped small particles. We define incoherent volume elements that describe the statistics of the random medium and formulate an order-of-scattering solution for the entire random medium. We apply the T-matrix formalism to compute the incoherent interactions of irregular particles in the sequence of scattering events in the Monte Carlo radiative transfer algorithm. The T-matrices for the volume elements of arbitrarily shaped particles are computed by the volume-integral-equation (VIE)-based T-matrix method. We show that the approximate solution is in agreement with the numerically exact VIE solution for a small spherical random medium. Finally, we demonstrate the importance of applying irregular particle shape models in the analysis of multiple scattering by a large random medium of non-spherical particles.

Interaction of psychotropic drugs with brain muscarinic cholinoceptors: similarities of biperiden with pirenzepine in receptor binding properties.

It is generally accepted that there are at least three different subtypes of muscarinic cholinoceptors, pirenzepine being considered a selective M1 antagonist. In the present study, a number of different types of psychotropic drugs have been compared with pirenzepine and atropine as reference antimuscarinic drugs regarding their affinities for rat brain muscarinic cholinoceptors with the help of in vitro receptor binding studies. The most potent drugs, inhibiting 3H-1-quinuclidinyl benzilate (3H-QNB) binding at subnanomolar concentrations, were the antimuscarinic drugs scopolamine and atropine. Biperiden, promethazine, pirenzepine and some tricyclic antidepressants (amitriptyline, doxepin) were the next potent drugs, with IC50-values between 8.4 nM and 190 nM. The inhibition curves were steep and parallel giving Hill coefficients close to unity in all but two drugs studied. These exceptions were biperiden and pirenzepine both with Hill coefficients about 0.55. Thus, in addition to pirenzepine also biperiden seems to bind to the M1 receptor selectively. Additional receptor and functional studies are warranted to further elucidate the possible similarities of these two drugs.