Crystal and molecular structures of pinacol ester of ferrocenyl-1,1′-diboronic acid

The molecular and crystal structure of pinacol ester of ferrocenyl-1,1′-diboronic acid was determined by X-ray crystallography. Dedicated to the 90th anniversary of the L. Ya. Karpov Institute of Physical Chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1289–1291, June, 2008.     

Automated measurement of birefringence: Development and experimental evaluation of the techniques

Traditional photoelasticity has started to lose its appeal since it requires a well-trained specialist to acquire and interpret results. A spectral-contents-analysis approach may help to revive this old, but still useful technique. Light intensity of the beam passed through the stressed specimen contains all the information necessary to automatically extract the value of retardation. This is done by using a photodiode array to investigate the spectral contents of the light beam. Three different techniques to extract the value of retardation from the spectral contents of the light are discussed and evaluated. An experimental system was built which demonstrates the ability to evaluate retardation values in real time.     

Bounds on quark mixing angles from the decay KL → μμ

We determine bounds on quark mixing angles in the standard six-quark model from an analysis of the decay $\text{K}{}_{\mathrm{L}}\text{→ μ}\text{μ}$. When combined with previous bounds from a Cabibbo fit and study of the $\text{K}{}^0\text{?}\text{K}{}^0$ transition amplitude, these can yield an improved upper limit on one of the angles.     

Prepeak in the structural factor. Inhomogeneous packings of Lennard-Jones atoms

This work reports on the effects of structural inhomogeneities within the models of spherical atomic packings on the radial distribution function (RDF) and the structural factor (SF). Models of inhomogeneous packings were constructed by removing some atoms from homogeneous packing according to a predetermined template. Thus various additional voids, leading to specific structural correlations of atoms on a middle scale (several atomic sizes), are introduced in the model. A dense noncrystalline packing of 27,000 Lennard-Jones atoms serves as the initial system. Three various templates were used, and models containing different fractions of additional voids were constructed with each of these templates. It is demonstrated that RDF is only slightly sensitive to such inhomogeneities; in contrast, the SF has additional peaks at small q, these peaks being notable even after removal of a small fraction of atoms. Some models yield a single narrow prepeak, which is akin to that observed in diffraction experiment for some glasses.     

Computer simulation study of intermolecular voids in unsaturated phosphatidylcholine lipid bilayers

Computer simulation of the liquid crystalline phase of five different hydrated unsaturated phosphadidylcholine (PC) lipid bilayers, i.e., membranes built up by 18:0/18:1omega9cis PC, 18:0/18:2omega6cis PC, 18:0/18:3omega3cis PC, 18:0/20:4omega6cis PC, and 18:0/22:6omega3cis PC molecules have been performed on the isothermal-isobaric ensemble at 1 atm and 303 K. (The notation n:domegapcis specifies the lipid tails: n refers to the total number of carbon atoms in the chain, d is the number of the methylene-interrupted double bonds, p denotes the number of carbons between the chain terminal CH(3) group and the nearest double bond, and cis refers to the conformation around the double bonds.) The characteristics of the free volume in these systems have been analyzed by means of a generalized version of the Voronoi-Delaunay method [M. G. Alinchenko et al., J. Phys. Chem. B 108, 19056 (2004)]. As a reference system, the hydrated bilayer of the saturated 14:014:0 PC molecules (dimyristoylphosphatidylcholine) has also been analyzed. It has been found that the profiles of the fraction of the free volume across the membrane exhibit a rather complex pattern. This fine structure of the free volume fraction profiles can be interpreted by dividing the membrane into three separate major zones (i.e., zones of the aqueous, polar, and apolar parts of the membrane) and defining five subzones within these zones according to the average position of various atomic groups in the membrane. The fraction of the free volume in the middle of the membrane is found to increase with increasing unsaturation of the sn-2 chain of the lipid molecule. This is due to the fact that with increasing number of methylene-interrupted double bonds the lipid tails become more flexible, and hence they do not extend to the middle of the membrane. It is found that there are no broad enough preformed channels in the bilayers through which small penetrants, such as water molecules, can readily go through; however, the existing channels can largely facilitate the permeation of these molecules.     

Crystal structure of holtite I

The crystal structure of As-containing holtite I is refined (Ital Structures diffractometer, 939 crystallographically independent reflections, anisotropic approximation, R = 0.047). The parameters of the orthorhombic unit cell are a = 4.695(1) Å, b = 11.906(3) Å, c = 20.38(3) Å, sp. gr. Pnma, Z = 4. On the whole, the structural formula obtained, (Si_2.43Sb_0.36As_0.21)BO₃[(Al_0.62Ta_0.26□)Al₂(Al_0.98□)₂(Al_0.94□)₂O₁₂](O,OH,□)_2.65, corresponds to the electron-probe analysis data. The statistical replacement of (Si,As)O₄ tetrahedra by pyramidal [SbO₃] groups is confirmed. The X-ray diffraction spectra of holtite I are compared with those of holtite II.     

The scattered radiation spectrum of a laser and the measurement of the electron concentration in a pulse plasma

The scattered radiation spectrum obtained in probing a high-frequency (hf) pulse plasma with a laser beam is discussed. The presence of satellites is attributed to Raman scattering at plasma vibrations occasioned by electron drift. The procedure, and results of measuring the electron density on the basis of the intensity of scattered radiation are described. Preliminary calibration of the apparatus was carried out by comparison with Rayleigh scattering in air and in argon.In conclusion we should iike to thank Dr. R. A. Demirkhanov for his interest in our study and Dr. I. A. Akhiezer for his useful comments on the results.     

Stability of implicit schemes on nonuniform grids

Implicit finite-difference approximations of the quasilinear conservation law are considered. Issues of stability and convergence are discussed, and an accuracy bound is obtained.Translated from Matematicheskie Modeli Estestvoznaniya, Published by Moscow University, Moscow, 1995, pp. 157–161.