Modelling photonic crystal fibers with localized functions

In this paper we present an overview of of the standard methods used when modelling photonic crystal fibers with Hermite-Gaussian functions, as well as a new variant of this modelling scheme, based solely on Hermite-Gaussian expansion series, which introduces the possibility of directly modelling fibers with finite claddings. We investigate the challenges and advantages of such a model and compare it to a proven modelling tool, namely the plane wave method.     

The synthesis and some NMR properties of 2,3-bis(diphenylphosphino)-6-phenyl-λ3-phosphinine

The synthesis, from 1,2,5-triphenylphosphole and bis(diphenylphosphino)acetylene, of 2,3-bis(diphenylphosphino)-6-phenyl-λ³-phosphinine, the first example of a λ³-phosphinine bearing phosphorus-containing side chains, is reported. This compound shows in its nmr spectrum the largest value of ³J_pp (178 Hz) yet reported for a system containing the P^III-C-C-P^III linkage. Evidence is presented which supports the idea that this extraordinarily large coupling arises as a result of geometrical factors which place the non-bonding electron pairs of the two side-chain P atoms in very close proximity to one another. Reactions of the λ³-phos-phinine with Ni(II) and Pt(II) compounds are briefly discussed in the context of the nmr properties of both the ligand and the complexes formed.     

Prediction of viscosities of hydrocarbon mixtures

A new model for prediction of the viscosities of hydrocarbons including oil and gas mixtures is presented. The model is based on the principle of corresponding states with methane and decane as reference components. The viscosity of a given component or mixture is determined from the reduced viscosities of the reference components using the molecular weight as an interpolation parameter.

The model has been used for prediction of viscosities of both pure components and mixtures over large pressure ranges and for reduced temperatures above 0.476. The results are in good agreement with the experimental data. The new model compares favorably with earlier published methods, which use only one reference component.

Finally, the model has been tested on data for 6 oil mixtures from the North Sea. The mean deviation based on 34 experimental points was 6.4 %.     

Mössbauer spectroscopy of an ordered phase (superstructure) of FeNi in an iron meteorite

Mössbauer and X-ray spectra for taenite lamellae from the iron meteorite Cape York show that the lamellae contain an ordered phase with the composition FeNi, and with the structure L10. This phase has not previously been detected in meteorites.     

A general organocatalytic enantioselective malonate addition to alpha,beta-unsaturated enones

A general enantioselective organocatalytic conjugate addition procedure of a variety of malonates to alpha,beta-unsaturated enone systems is presented. The reaction is efficiently catalysed by the pyrrolidinyl tetrazole catalyst 1. Cyclic, acyclic and aromatic enones can be used and the reaction with ethyl malonates 3 b provides the Michael addition products in high yields with good to excellent enantioselectivities. Since only 1.5 equivalents of malonate are used as a reagent, the reaction is readily scaled and practical to operate. Furthermore, the malonate addition products can be easily mono decarboxylated without loss in enantiomeric excess by enzymatic or sodium hydroxide mediated methods.     

Temperature-induced intermicellization and contraction in aqueous mixtures of sodium dodecyl sulfate and an amphiphilic diblock copolymer

Aqueous solutions of a thermoresponsive amphiphilic diblock copolymer, containing poly(N-isopropylacrylamide), in the presence of the anionic sodium dodecyl sulfate (SDS) surfactant can undergo a temperature-induced transition from loose intermicellar clusters to collapsed core–shell nanostructures. The polymer–surfactant mixtures have been characterized with the aid of turbidity, small-angle neutron scattering (SANS), intensity light scattering (ILS), dynamic light scattering (DLS), shear viscosity, and rheo-small angle light scattering (rheo-SALS). In the absence of SDS, compressed intermicellar structures are formed at intermediate temperatures, and at higher temperatures further aggregation is detected. The SANS results disclose a structure peak in the scattered intensity profile at the highest measured temperature. This peak is ascribed to the formation of ordered structures (crystallites). In the presence of a low amount of SDS, a strong collapse of the intermicellar clusters is observed at moderate temperatures, and only a slight renewed interpolymer association is found at higher temperatures because of repulsive electrostatic interactions. Finally, at moderate surfactant concentrations, temperature-induced loose intermicellar clusters are detected but no shrinking was registered in the considered temperature range. At a high level of SDS addition, large polymer–surfactant complexes appear at low temperatures, and these species are compressed at elevated temperatures. The rheo-SALS results show that the transition structures are rather fragile under the influence of shear flow.     

Aqueous Mixtures of a Trisiloxane Surfactant and Oil Studied by SANS and NMR Self-diffusion: Effect of Temperature and Oil Concentration

Samples of a poly(ethylene oxide) trisiloxane surfactant, water, and decane have been investigated using pulsed field gradient NMR (PGSE NMR) and small-angle neutron scattering (SANS) to determine the solution structure. The surfactant/water weight ratio has been kept constant at a value of 3/2, with variation of the oil (decane) content. In the neutron scattering measurements the temperature was varied from 23 °C up to the phase separation limit for these systems. The combined NMR and SANS data show that on addition of decane, the system exists as a hexagonal phase of cylindrical decane-containing micelles at all temperatures investigated. The addition of decane changes significantly the values for the structure parameters in the system, inducing an increase in periodicity of 12–15 ?. By substitution of decane with its deuterated equivalent, decane-d₂₂, it was possible to obtain detailed information on the structural organization of the oil component in this ternary mixture.     

Revisiting the structure of the p(4 x 4) surface oxide on Ag(111)

Scanning tunneling microscopy (STM) and density-functional theory are used to reexamine the structure of the renowned p(4 x 4)-O/Ag(111) surface oxide. The accepted structural model [C. I. Carlisle, Phys. Rev. Lett. 84, 3899 (2000)10.1103/PhysRevLett.84.3899] is incompatible with the enhanced resolution of the current STM measurements. An "Ag6 model" is proposed that is more stable than its predecessor and accounts for the coexistence of the p(4 x 4) and a novel c(3 x 5log3)rect phase. This coexistence is an indication of the dynamic complexity of the system that until now has not been appreciated.     

Numerical analysis of the rotational relaxation time of spectrin segments and spectrin heterodimer in dilute aqueous solution

The rotational relaxation time for different models of the spectrin αβ-heterodimer and spectrin subunits were obtained through numerical simulation making use of the so-called rigid-body approximation. Based on information on the helix structure of the 106 aminoacids in the repeating motif of spectrin, three different models with varying degree of refinement were set up to represent the spectrin subunits: the two-bead, the many-bead and the shell model. For one- and two-subunit spectrin the relaxation time was found to be 20 ± 4 ns and 92 ± 5 ns, respectively. The last result conforms well with available experimental data from transient electric birefringence measurements. For the αβ-heterodimer two different models were applied: a chain of beads (pearl necklace model) and a more refined so-called San necklace model. Using the San necklace model, the relaxation time was found to be in the range of 9 to 18 μs (depending on the flexibility of the joint), which is in accordance with what has been obtained from intrinsic viscosity measurements, but considerably higher than experimental data from measurements of transient electric birefringence.     

A Mössbauer study of an impactite from the Monturaqui crater

The iron mineralogy of samples of the Monturaqui impactite has been studied by Mössbauer spectroscopy. Magnetite, maghemite, goethite and a ferrous glass phase were identified. In a magnetic separate a bcc-structured iron-nickel alloy was identified in addition to the oxide phases. The oxides have formed by weathering of iron-nickel alloys.