Low loss, low dispersion and highly birefringent terahertz porous fibers

We demonstrate that porous fibers in addition to low loss and high confinement, have near zero dispersion for 0.5-1 THz resulting in reduced terahertz signal degradation compared to microwires. We also show for the first time that these new fibers can be designed, introducing asymmetrical sub-wavelength airholes within the core, to achieve high birefringence ≈0.026. This opens up the potential for realization of novel polarization preserving fibers in the terahertz regime.     

Polymer modification using difluoromethane (HFC 32) and carbon dioxide

The infusion of difluoromethane (HFC 32) and CO₂ into polystyrene and polyethylene has been characterized using a quartz crystal microbalance technique over a range of temperatures and pressures. The results were adequately modeled by Flory‐Huggins theory. Significant plasticization was observed in the polymeric materials and it is shown that manipulation of the experimental temperature, pressure, and rate of depressurisation can cause significant changes in the morphology of the samples. It is demonstrated for the first time how rate constant data for the kinetics of gas sorption can be extracted quickly and easily from in situ quartz crystal microbalance measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1072–1083, 2006     

Finding synthetically versatile and common intermediates for multiple useful products with the aid of a synthesis design system

With the aid of a synthesis design system, we searched for common intermediates in routes to sets of target molecules. Finding such common intermediates will be a great help in constructing cost-effective synthetic routes. We tried to look for new common intermediates with 24 investigational or commercially produced antidepressants as target molecules. Most of the common intermediates were usually found to lead to more than two targets.     

The non-perpendicular and non-parallel alkyne bridge in W2(μ-C2H2)(μ-OCH2Bu)2(OCH2Bu)6

The bonding in the ethyne adduct W₂(μ-C₂H₂)(μ-ONp)₂(ONp)₆ (Np=CH₂^tBu) has been examined by various computational methods [Extended Hückel (EHMO), Fenske–Hall, and Gaussian 92 RHF (Restricted Hartree–Fock) and density functional (Becke-3LYP) calculations] employing the model compound W₂(μ-C₂H₂)(μ-OH)₂(OH)₆. EHMO and Fenske–Hall calculations suggest, based on total orbital energy, that a μ-parallel ethyne geometry should have the lowest energy, although traditional frontier orbital arguments agree with the observance of a skewed acetylene bridge. Gaussian 92 computations reproduce the non-perpendicular/non-parallel μ-C₂H₂ geometry in close agreement to that observed in the solid-state (X-ray) structure, which leads us to suggest that the distortion is not sterically imposed by the attendant alkoxide ligands. The observed geometry can be rationalized in terms of Jahn–Teller distortional stabilization from either the μ-parallel or μ-perpendicular mode, i.e., the geometry is favored on electronic grounds, though the potential energy surface is rather shallow. These results are discussed in terms of previous studies of the addition of alkynes to d³–d³ dinuclear complexes of tungsten and in terms of relationships between d²-W(OR)₄ and d⁸-Os(CO)₄ fragments.     

1-(Di­bromo­methyl)-4-methoxy-2-methyl­benzene

The title compound, C₉H₁₀Br₂O, is a major product of the radical bromination of 4-methoxy-1,2-di­methyl­benzene. Each Br atom is involved in a close contact with the O atom of a neighbouring mol­ecule, forming a geometry that is suggestive of weak intermolecular OBr charge-transfer interactions.     

Scaling in small-world resistor networks

We study the effective resistance of small-world resistor networks. Utilizing recent analytic results for the propagator of the Edwards–Wilkinson process on small-world networks, we obtain the asymptotic behavior of the disorder-averaged two-point resistance in the large system-size limit. We find that the small-world structure suppresses large network resistances: both the average resistance and its standard deviation approaches a finite value in the large system-size limit for any non-zero density of random links. We also consider a scenario where the link conductance decays as a power of the length of the random links, l⁻. In this case we find that the average effective system resistance diverges for any non-zero value of .     

The set of values of b for which there exist block designs with b blocks

Let B denote the set of values of b for which there exists a block design with b blocks and for k3, let B_k denote the subset of B determined by the designs with block size k. We present some information about B and the sets B_k. In particular, we discuss, for certain integers h, the question as to whether there exist integers k and k^′ such that the equation b^′=b+h has infinitely many solutions b,b^′ satisfying bB_k and b^′B_k^′. The study is restricted to the case λ=1.     

Synthesis of a new zwitterionic cyclopentadienyl-imidazolium compound and isolation of the 3,3′-(trans-3,5-cyclopentenyl)di(1-tert-butylimidazolium)bromide intermediate

The new zwitterionic compound 1-tert-butylimidazolium-cyclopentadienylide, shown to have a polar ground state and a non-polar fulvene-like excited state, has been synthesised and the intermediate 3,3′-(trans-3,5-cyclopentenyl)di(1-tert-butylimidazolium)bromide isolated and structurally characterised.