Spatial desynchronization of glycolytic waves as revealed by Karhunen-Loeve analysis

The dynamics of glycolytic waves in a yeast extract have been investigated in an open spatial reactor. At low protein contents in the extract, we find a transition from inwardly moving target patterns at the beginning of the experiment to outwardly moving spiral- or circular-shaped waves at later stages. These two phases are separated by a transition phase of more complex spatiotemporal dynamics. We have analyzed the pattern dynamics in these three intervals at different spatial scales by means of a Karhunen-Loeve (KL) decomposition. During the initial phase of the experiment, the observed patterns are sufficiently described by the two dominant KL modes independently of the spatial scale. However, during the last stage of the experiment, at least 6 KL modes are needed to account for the observed patterns at spatial scales larger than 3 mm, while for smaller scales, 2 KL modes are still sufficient. This indicates that in the course of the experiment, the local glycolytic oscillators become desynchronized at spatial scales larger than 3 mm. Possible reasons for the desynchronization of the glycolytic waves are discussed.     

Study of gas-fluidization dynamics with laser-polarized 129Xe

We report initial NMR studies of gas dynamics in a particle bed fluidized by laser-polarized xenon (129Xe) gas. We have made preliminary measurements of two important characteristics: gas exchange between the bubble and emulsion phases and the gas velocity distribution in the bed. We used T2* contrast to differentiate the bubble and emulsion phases by choosing solid particles with large magnetic susceptibility. Experimental tests demonstrated that this method was successful in eliminating 129Xe magnetization in the emulsion phase, which enabled us to observe the time dependence of the bubble magnetization. By employing the pulsed field gradient method, we also measured the gas velocity distribution within the bed. These results clearly show the onset of bubbling and can be used to deduce information about gas and particle motion in the fluidized bed.     

Mineral?le

Ohne Zusammenfassung     

Some Problems Concerning the Mechanism of the Isotactic Polymerization of Methyl Methacrylate Initiated by Organomagnesium Compounds in Toluene Solution—Application of Modified Dilatometer and NMR Methods

A dilatometer capable of being rapidly filled with monomer and initiator solutions mixed under carefully controlled conditions and a modification of an NMR T₁ program, adapted to store and display on recall the results of frequent sweeps at 30-s intervals of relevant proton resonances of a polymerizing mixture, are reported. These techniques have been applied to the identification of the optimum conditions for efficient, initiation of isotactic polymerization and investigation of the mechanism of propagation. It is shown that heat treatment does not remove the coordinated THF (1 molecule per RMg group) when toluene-soluble “tBuMgBr” or “PhMgBr” initiators are prepared and that the optimum THF concentration is slightly in excess of this. The nature of the solute in the toluene-soluble initiator solutions is discussed. The kinetics of the polymerization change from internal zero order to internal order of one with respect to monomer as the temperature increases from 225–275 K. This is consistent with a previously proposed mechanism in which propagation proceeds through a complex between monomer and the active center.     

Synthesis and structural characterization of a nickel(II) precatalyst bearing a β‐triketimine ligand and study of its ethylene polymerization performance using response surface methods

The reaction of N‐(4‐(mesitylamino)pent‐3‐en‐2‐ylidene)‐2,4,6‐trimethylbenzenamine ( 1 ) with n‐butyl lithium and then with N‐(2,4,6‐trimethyl‐phenyl)‐acetimidoyl chloride yields a new β‐triketimine ligand, N‐(4‐(mesitylamino)‐3‐(1‐(mesitylimino)ethyl)pent‐3‐en‐2‐ylidene)‐2,4,6‐trimethylbenzenamine, 2 . The addition of 2 to nickel (II) dibromide 1,2‐dimethoxyethane (NiBr₂(DME)) in the presence of [Na]⁺[3,5‐(CF₃)₄C₆H₃]₄B]^? (NaBAr'₄) gives a five‐coordinate dimeric complex [( 2 .NiBr)₂].2 [(BAr'₄)], 3 . The structure of 3 has been determined by single crystal X‐ray diffraction. This complex generates catalytically active species for the homopolymerization of ethylene in combination with methylaluminoxane to produce elastomeric, branched polyethylene. The effect of factors (temperature, pressure, and cocatalyst to catalyst molar ratio (CC)) on the polymerization process has been investigated using regression models of responses (catalyst activity, crystallinity, and weight‐average molecular weight of polymer (M_w)) and visualized via the response surface method (RSM). Activity and M_w responses show a second‐order variation with temperature and vary linearly with pressure. Conversely, crystallinity follows a second‐order model while varying temperature, pressure, and CC. Furthermore, a set of polymerization conditions for reaching desirable responses was predicted and then experimentally verified. The activities achieved challenge the best reported activities for Ni(II) catalysts with β‐connected imine ligand supports, but fall short of those for α‐diimines. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Nanocomposites of ferroelectric liquid crystals and FeCo nanoparticles: towards a magnetic response via the application of a small electric field

ABSTRACT

We study a nanocomposite consisting of a ferroelectric liquid crystal and a magnetic nanoparticle in order to explore the possibility of using it as a magnetic resonant imaging contrast agent which will measure a field of 20 V/m. To achieve this we use the ferroic properties exhibited by the nanocomposite. We used the ferroelectric liquid crystal 2-(4-((2-fluorooctyl)oxy)phenyl)-5-(octyloxy)pyrimidine mixed with FeCo nanoparticles nominally 2–3 nm in diameter in concentrations of 0.56, 4.3 and 10.8 wt%. The 10.8 wt% sample was chosen for our study because the nanoparticles acted as a lubricant for the ferroelectric liquid crystal. This concentration yields nanoparticle clusters in about 5 ? 10 μm diameter spherulites. An electric field as low as 5V/cm is enough to turn and realign the spherulites where the particles are contained. We estimate the value of the magnetic in a spehrulite and associate it to the number of spherulites aligned as a function of electric field. We find thus that we can achieve low electric fields.     

Isotactic and stereoblock poly(methyl methacrylates) produced by butylmagnesium initiators

The use of tert-, sec-, iso- and normal-butylmagnesium bromides and chlorides in toluene, tetrahydrofuran and mixed solvents to prepare Bernoullian, stereoblock and isotactic poly(methyl methacrylate). PMMA, and the factors controlling the stereochemistry are described. By careful control of solvent composition, highly isotactic polymer can be prepared with all the butylmagnesium bromides, but none of the corresponding dibutylmagnesiums. The halide content does not influence stereospecificity when it is in excess of the Grignard stoichiometry but it influences the mol. wt distribution and retards the polymerization. The mol. wt distributions are usually polymodal and dependent on the same factors that control stereospecificity. The effect of THF concentration on stereospecificity operates in a manner quite distinct from its effect on complex concentration and rate. The concentration of residual THF in toluene-rich solution determines the type of initiation and propagating species that prevail. Structures are proposed for those responsible for stereospecific initiation and propagation. It is concluded that tert-butylmagnesium bromide is the most reliable and robust initiator for preparing isotactic PMMA.