Kinetics of supramolecular crystallization of concentrated suspensions of monodisperse spherical silica particles

The kinetics of supramolecular crystallization of concentrated suspensions is three-dimensional and follows the Avrami-Erofeev equation: A=1-exp[-(kt)^m], where m=4. The rate constant k is proportional to the probability of the appearance of a crystallization center in unit volume in unit time and the linear crystal growth rate, which is determined experimentally.     

Determination of enantiomeric purity of 1-substituted 3-amino-1,2-dicarba-<Emphasis Type="Italic">closo</Emphasis>-dodecaboranes by HPLC on chiral stationary phases

A determination of enantiomeric purity of 1-substituted (Me, Ph, and Prⁱ) 3-amino-1,2dicarba-closo-dodecaboranes by HPLC on chiral Chiralcel OD-H and Chiralpac AD stationary phases involving preliminary phthaloylation of 3-aminocarboranes has been suggested as a general method.     

Haloalkynylation of norbornadiene with haloacetylenes activated with a trifluoroacetyl or ethoxalyl group

Reactions of norbornadiene with haloacetylenes activated with a trifluoroacetyl or ethoxalyl group proceed as stereospecific conjugated exo-addition of the alkynyl substituent and the halogen atom to the double bond of norbornadiene.     

Carboranyl phosphites: the electronic effect in the Suzuki- Miyaura reaction

Isomeric carborane-containing phosphite ligands possessing different electronic properties have been synthesized. Their use in the Pd-catalyzed Suzuki-Miyaura reaction involving activated aryl bromides showed that phosphite with 9-o-carborane substituent has proved more efficient, with carboranyl phosphite having 1-m- carborane fragment being more efficient in the reactions with nonactivated aryl bromides.     

Self-sustained oscillations in systems with delay under irregularly varying excitation conditions

A mathematical model of a system consisting of two coupled chaotic delay subsystems is presented. Instead of constant initial conditions in the form of a single impetus to excite the subsystems, continuous irregular oscillations are used that simulate intrinsic noise and continue acting on self-sustained oscillations after their excitation. An equation of an autonomous subsystem with regard to feedback variation is derived. It is shown that, when an autonomous subsystem is excited by irregular oscillations, chaotic motions become stochastic. In this case, the intensity of oscillations simulating intrinsic noise increases, suppressing self-sustained oscillations and providing the regenerative amplification of irregular oscillations. Interaction of coupled oscillations for identical and nonidentical subsystems is considered for the case of different noiselike initial conditions. It is found that interacting oscillations are not completely identical even if the parameters of the subsystems are the same.     

Observation of a superfluid component within solid helium

We demonstrate by neutron scattering that a localized superfluid component exists at high pressures within solid helium in aerogel. Its existence is deduced from the observation of two sharp phonon-roton spectra which are clearly distinguishable from modes in bulk superfluid helium. These roton excitations exhibit different roton gap parameters than the roton observed in the bulk fluid at freezing pressure. One of the roton modes disappears after annealing the samples. Comparison with theoretical calculations suggests that the model that reproduces the observed data best is that of superfluid double layers within the solid and at the helium-substrate interface.