Olefin polymerization by cyclopentadienyltris(dimethylamido)titanium(IV) complexes

Several titanium(IV) complexes of the type Cp′Ti(NMe₂)₃ [Cp′ = cyclopentadienyl ( 1 ), (dimethylaminoethyl)cyclopentadienyl ( 2 ), indenyl ( 3 ), and pentamethylcyclopentadienyl ( 4 )] were prepared, and their catalytic properties in the polymerization of α‐olefins were examined. Complexes 1 and 2 catalyzed the polymerization of ethylene in the presence of methylaluminoxane with a much higher activity than 3 or 4 . Complexes 3 and 4 polymerized ethylene with an activity similar to that of CpTiCl₃ ( 6 ). The preactivation of 2 , 3 , or 4 with trimethylaluminum (TMA) resulted in an increase in ethylene polymerization activities. Also, 1 and 2 were successfully used as ethylene/1‐hexene copolymerization catalysts, producing polymers with various amounts of 1‐hexene incorporation, depending on the amount of 1‐hexene in the feed mixture. Complex 1 likewise effectively polymerized styrene with a higher activity and higher syndiospecificity than the other three catalysts. Complexes 3 and 4 polymerized styrene with low syndiospecificity, whereas 2 produced only atactic polystyrene. The preactivation of 3 or 4 with TMA resulted in an increase in styrene polymerization activities and increased the syndiotacticity percentage of the polymers produced. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 313–319, 2001     

The opportunistic transmission of wireless worms between mobile devices

The ubiquity of portable wireless-enabled computing and communications devices has stimulated the emergence of malicious codes (wireless worms) that are capable of spreading between spatially proximal devices. The potential exists for worms to be opportunistically transmitted between devices as they move around, so human mobility patterns will have an impact on epidemic spread. The scenario we address in this paper is proximity attacks from fleetingly in-contact wireless devices with short-range communication range, such as Bluetooth-enabled smart phones.An individual-based model of mobile devices is introduced and the effect of population characteristics and device behaviour on the outbreak dynamics is investigated. The model uses straight-line motion to achieve population, though it is recognised that this is a highly simplified representation of human mobility patterns. We show that the contact rate can be derived from the underlying mobility model and, through extensive simulation, that mass-action epidemic models remain applicable to worm spreading in the low density regime studied here. The model gives useful analytical expressions against which more refined simulations of worm spread can be developed and tested.     

Finite-aperture effects for Fourier transform systems with convergent illumination. Part II: 3-D system analysis

One of the most important optical signal processing operations is the optical Fourier transform (OFT). Of the arrangements for implementation of the OFT, perhaps the most flexible is that for the scaled optical Fourier transform (SOFT), as it allows control over the scale of the output Fourier transform distribution. By means of an analysis in cylindrical coordinates, we examine some of the practical limits introduced by the use of a thin lens of finite aperture in the implementation of the SOFT. Using simple rules of thumb that are based on an examination of the phase and magnitude deviations from the ideal (infinite-lens) diameter case, we define a volume inside the geometric shadow, which we refer to as a sub-geometric shadow. We then show that inside this sub-geometric shadow errors introduced by diffraction can be quantified.     

Muonium adducts of benzaldehyde: Structural correlation with nitroxides

We have formed adduct radicals (ArCHOMu\bullet) by muonium addition to the carbonyl group of benzaldehyde and its derivatives. The muon coupling is found to be highly sensitive to the nature of substituents in the benzene ring, being increased by electron releasing groups. Similarly, the ¹⁴N coupling in a series of nitroxides [ArN(O\bullet)OSiEt₃], measured using ESR spectroscopy, is increased by electron releasing substituents and a linear correlation is found between the two; their connected nature is discussed. For the radical derived from benzaldehyde itself, a strong dependence is also found on the solvent in which it is solved. We suggest that this may be used in the study of solvent effects, particularly H‐bonding, pertinent to organic and bioorganic media. This revised version was published online in August 2006 with corrections to the Cover Date.     

The chelation ofo-nitrosopyrimidinols. I

Summary A spectrophotometric study has been made on the iron-2,6-diamino-5-nitroso-4-pyrimidinol reaction. The study shows that the reaction ratio is 4 to 1 reagent to iron(II). The blue complex has an absorption maximum at 653 nm and a molar absorptivity of 2.0·10⁴ l.mole^–1.cm^–1.

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Zusammenfassung Die Reaktion von Eisen(II) mit 2,6-Diamino-5-nitroso-4-pyrimidinol wurde spektrophotometrisch untersucht. Die Komplexbildung findet im Molverhältnis Reagens: Eisen=41 statt. Der blaue Komplex hat ein Absorptionsmaximum bei 653 nm und eine molare Extinktion von 2,0·10⁴ l.Mol^–1.cm^–1.

     

Application of pattern recognition and feature extraction techniques to volatile constituent metabolic profiles obtained by capillary gas chromatography

The applicability of threshold logic units, a form of nonparametric pattern recognition, to the processing of metabolic profile data obtained by high-efficiency glass capillary column gas chromatography has been investigated. The test data included profiles of the volatile constituents of urine from normal individuals and from individuals with diabetes mellitus. A feature extraction algorithm allowed for dimensionality reduction and indicated the constituents most important in the normal versus pathological distinction. With an optimum number of dimensions, a normal versus pathological prediction rate of 93.75% was achieved. Gas chromatography-mass spectrometry was utilized to identify important profile constituents.     

Electric fields in zeolites: fundamental features and environmental implications

A critical review of zeolites and their use in practical applications is presented. Specifically-considered are their role as media for selective light-induced oxidations using molecular O₂, and the relationship between this phenomenon and the surface electric fields that exist in zeolites. Methods for the determination of the strength of zeolite surface fields are discussed using sorbed molecules such as CO (with IR detection), spin-probes, di-tert-butyl nitroxide, and NO (measured using EPR spectroscopy). Relationship between the surface fields and molecular reorientation energetics for free radicals sorbed in zeolites, obtained using muonium as a spin-label, is explored. Finally, results obtained from exposing the naturally occurring zeolite, clinoptilolite, to high energy electrons as a means for activating materials toward selective removal of radioactive caesium and strontium cations from wastewaters of nuclear power plants are presented.     

Spectral Dimension of Liouville Quantum Gravity

This paper is concerned with computing the spectral dimension of (critical) 2d-Liouville quantum gravity. As a warm-up, we first treat the simple case of boundary Liouville quantum gravity. We prove that the spectral dimension is 1 via an exact expression for the boundary Liouville Brownian motion and heat kernel. Then we treat the 2d-case via a decomposition of time integral transforms of the Liouville heat kernel into Gaussian multiplicative chaos of Brownian bridges. We show that the spectral dimension is 2 in this case, as derived by physicists (see Ambjørn et al. in JHEP 9802:010, 1998) 15 years ago.