Quasielastic light-scattering studies of aqueous biliary lipid systems. Mixed micelle formation in bile salt-lecithin solutions

From measurements of the autocorrelation function and time-averaged intensity of light scattered from aqueous bile salt-lecithin solutions, we deduced the mean hydrodynamic radius (Rh), shape, and polydispersity of bile salt-lecithin mixed micelles as functions of bile salt species, lecithin to bile salt (L/BS) molar ratio, total lipid concentration (0.625-10 g/dL), temperature (20-60 degrees C), and NaCl concentration (0.15-0.6 M). Our data suggest that at low L/BS ratios (0 to approximately 0.6) simple bile salt micelles coexist in varying proportions with minimum-sized mixed micelles (Rh, 18-35 A). These solutions are highly polydisperse and display features dependent upon the particular bile salt species. At high L/BS ratios (greater than 0.6), only mixed micelles are present, and their sizes increase markedly (Rh, 20 leads to 300 A) with increases in L/BS ratio and appear to diverge as the lecithin-bile salt phase limit is approached. The shape of the mixed micelles as deduced from light-scattering measurements and confirmed by transmission electron microscopy is disklike. The radii of the disks, however, are not compatible with Small's model of mixed micellar structure [Small, D.M. (1967a) Gastroenterology 52, 607-a1 but are consistent with a new model proposed here in which bile salts and lecithin interact to form a mixed bilayer disk which is surrounded on its perimeter by bile salts. The inclusion of bile salts in a fixed stoichiometry within the interior of the bilayers is shown to provide a quantitative explanation for the divergence of the mixed micellar sizes, their temperature dependence, and the origin of the lecithin-bile salt phase limit. The influence of total lipid concentration on both mixed micellar size and the lecithin-bile salt phase limit is explained by the "mixed disk" model by taking account of the equilibrium between mixed micelles and bile salt monomers in the intermicellar solution. By use of this concept, deductions of the intermicellar bile salt concentration in taurocholate-lecithin solutions are made and are shown to vary as a function of mixed micellar size and temperature. The range of values obtained, 3-6 mM, is comparable in magnitude to the critical micellar concentration of the pure bile salt.     

Effect of Co on the magnetism and phase stability of lithiated manganese oxides

We present first-principles calculations of the relative energies of various phases of lithiated manganese oxides with and without Co. We use the ultrasoft pseudopotential method as implemented in the Vienna ab initio simulation package (VASP). The calculations employ the local spin density approximation (LSDA) as well as the generalized gradient approximation (GGA). We consider monoclinic and rhombohedral structures in paramagnetic, ferromagnetic and antiferromagnetic (AF3) spin configurations. Spin-polarization significantly lowers the total energy in all cases. The effect of Co on the stability of these phases is discussed.     

A study of the discharge characteristics of lead—acid batteries

A theoretical analysis of the electrolyte concentration distribution and current distribution in the porous lead dioxide electrode has been made by application of Fick's second law which was combined with approximate mass balances. The macrohomogeneous model for porous electrodes was used. The parameters in the models were determined experimentally for the lead dioxide battery plates and the special experimental cylindrical electrodes investigated. Numerical solutions for special cases are discussed. Theoretical results are in good agreement with experimental determinations. According to laser interferometry analysis the assumption of convectionless diffusion is, in practice, a good approximation in most cases.Theoretical studies of the local overpotential show that the utilizable capacity is determined by the decreasing ionic concentration of the electrolyte because the electrode reaction takes place mainly in the outer layers of the electrode, if the discharge current has a high value, e.g., full discharge time is less than 10 min.     

Electroencephalographic study on experimental brain edema induced by triethyltinsulfate (author's transl)

The electroencephalographic effects of several doses of a brain edema inducing agent, triethyltinsulfate (TET), was studied by implanted epidural electrodes in cats. The effect of TET on the central nervous system was found to have two phases: 1. a six hours' acute toxic phase following TET administration, 2. An edematic phase developing on the 2nd to the 4th day. Similarly to our earlier observations brain edema induced by TET was found to be dose-dependent, as shown by EEG-s, and their analysis performed by computation.     

Molecular dynamics simulation of low energy displacement cascades in Cu

Molecular dynamics computer simulations have been performed to study properties of low-energy (< 500 eV) displacement cascades in Cu. Various aspects of the time development of cascades are considered including instantaneous number of Frenkel pairs, partitioning of kinetic and potential energies, distribution of atom kinetic energies, cascade expansion rate, and Frenkel pair distributions. The anisotropy of the threshold energy for Frenkel-pair production is interpreted in terms of “branching”. Replacement sequences and the damage function are discussed based on analysis of events corresponding to 18 recoil directions. The damage function exhibits a plateau at $\text{v ~ 0.5}$ Frenkel pairs extending from 25–150 eV; at higher recoil energies the onset of multiple defect production is much slower than predicted by the modified Kinchin-Pease model.     

Habit Learning and the Genetics of the Dopamine D? Receptor: Evidence From Patients With Schizophrenia and Healthy Controls.

In this study, the authors investigated the relationship between the Ser9Gly (SG) polymorphism of the dopamine D? receptor (DRD3) and striatal habit learning in healthy controls and patients with schizophrenia. Participants were given the weather prediction task, during which probabilistic cue-response associations were learned for tarot cards and weather outcomes (rain or sunshine). In both healthy controls and patients with schizophrenia, participants with Ser9Ser (SS) genotype did not learn during the early phase of the task (1-50 trials), whereas participants with SG genotype did so. During the late phase of the task (51-100 trials), both participants with SS and SG genotype exhibited significant learning. Learning rate was normal in patients with schizophrenia. These results suggest that the DRD3 variant containing glycine is associated with more efficient striatal habit learning in healthy controls and patients with schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)