Coaxial electrospinning of microfibres with liquid crystal in the core

Liquid crystal containing composite fibres were produced via coaxial electrospinning, demonstrating that this technique can be used for producing new functional fibres and/or to study the impact of extreme confinement on liquid crystal phases.     

Determination of absolute configuration using density functional theory calculations of optical rotation and electronic circular dichroism: chiral alkenes

In principle, the absolute configuration (AC) of a chiral molecule can be deduced from its optical rotation (OR) and/or its electronic circular dichroism (ECD). In practice, this requires reliable methodologies for predicting OR and ECD. The recent application of ab initio time-dependent density functional theory (TDDFT) to the calculation of transparent spectral region OR and ECD has greatly enhanced the reliability with which these phenomena can be predicted. TDDFT calculations of OR and ECD are being increasingly utilized in determining ACs. Nevertheless, such calculations are not perfect, and as a result, ACs determined are not 100% reliable. In this paper, we examine the reliability of the TDDFT methods in the case of chiral alkenes. Sodium d line specific rotations, [alpha]D, are predicted for 26 conformationally rigid alkenes of known AC, ranging in size from 5 to 20 C atoms, and with [alpha]D values in the range of 0-500. The mean absolute deviation of predicted [alpha]D values from experimental values is 28.7. With one exception, beta-pinene, the signs of [alpha]D are correctly predicted. Errors in calculated [alpha]D values are approximately random. Our results define a "zone of indeterminacy" within which calculated [alpha]D values cannot be used to determine ACs with >95% confidence. TDDFT ECD spectra are predicted for eight of the alkenes and compared to experimental spectra. Agreement ranges from modestly good to poor, leading to the conclusion that TDDFT calculations of ECD spectra are not yet of sufficient accuracy to routinely provide highly reliable ACs. TDDFT OR calculations for two conformationally flexible alkenes, 3-tert-butylcyclohexene and trans-4-carene, are also reported. For the former, predicted rotations are incorrect in sign over the range 589-365 nm. It is possible that the AC of this molecule has been incorrectly assigned.     

An analysis of the current-voltage characteristics of thin film front wall illuminated and back wall illuminated liquid junction and schottky barrier solar cells

Analytical expressions for the current-voltage characteristics of thin film front illuminated and back illuminated liquid junc tion solar cells have been derived as a function of film thickness. The usual assumptions of a flat minority carrier quasi Fermi level across the semiconductor depletion region or a constant minority carrier concentration at the semiconductor surface have not been made. Depletion layer recombination is included in both expressions. The effects of various parameters, including thickness and back recombination velocity, are determined for both types of devices.     

Dissociative ionization of molecules in intense laser fields

Accurate and efficient grid based techniques for the solution of the time-dependent Schrödinger equation for few-electron diatomic molecules irradiated by intense, ultrashort laser pulses are described. These are based on hybrid finite-difference, Lagrange mesh techniques. The methods are applied in three scenarios, namely H₂ ⁺ with fixed internuclear separation, H₂ ⁺ with vibrating nuclei and H₂ with fixed internuclear separation and illustrative results presented.Received: 19 November 2002, Published online: 24 April 2003PACS: 02.60.Cb Numerical simulation; solution of equations - 02.70.Bf Finite-difference methods - 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 33.80.-b Photon interactions with molecules     

The influence of interlayer asymmetry on the magnetospectroscopy of bilayer graphene

We present a self-consistent calculation of the interlayer asymmetry in bilayer graphene caused by an applied electric field in magnetic fields. We show how this asymmetry influences the Landau level spectrum in bilayer graphene and the observable inter-Landau level transitions when they are studied as a function of high magnetic field at fixed filling factor as measured experimentally in [E.A. Henriksen, Z. Jiang, L.-C. Tung, M.E. Schwartz, M. Takita, Y.-J. Wang, P. Kim, and H.L. Stormer, Phys. Rev. Lett. 100 (2008), 087403]. We also analyse the magneto–optical spectra of bilayer flakes in the photon-energy range corresponding to transitions between degenerate and split bands of bilayers.     

Tutorial: The modelling of chemical processes

The modelling of chemical processes entails the computation of the concentration profiles of all reaction species as a function of the reaction time. The basis for the calculations is the system of differential equations (ODE's) that is defined by the reaction mechanism. Most textbooks on chemical kinetics concentrate on those few reaction mechanisms that lead to ODE's with explicit solutions. In this tutorial, we demonstrate that numerical integration is a viable alternative, that it can be applied to any mechanism, and that it is easy to do so. Matlab example programs illustrate the concepts and they allow the reader to explore the effects of changing conditions such as initial concentrations or rate constants etc. Example reaction mechanisms include a zero-th order enzymatic reaction and reactions at non-constant temperature and pH.     

Diffusion within ultrathin, dense nanoporous silica films

In this work the origin of permselectivity in dense silica films which possess a pore structure with pore sizes commensurate with the molecular size of the diffusing gas species is investigated. Much of the recently reported work in this field has involved the development of composite membrane films, and while it is generally assumed that the transport process of the gas species within the selective layer of these films is activated in nature, there are anomalies with this simplified picture. In this paper a new model is developed which, for the first time, explains the permselective behavior of the thin selective coatings ubiquitous to membrane separation processes. The model involves the existence of two primary transport domains within the solid film, one of which rapidly conducts the permeating gas (under non-Fickian conditions), while the second domain involves a slow diffusion mode characterized by normal Fickian transport. To validate the model, molecular dynamics simulations are conducted for diffusion of a number of simple gases (He, N(2), and CO(2)) within silica glasses over a range of solid densities. The silica media employed in these studies are based on a novel approach developed in this work for the construction of three-dimensionally periodic atomistic structures of silica of arbitrary density in which network bond connectivity is ensured. The results obtained from this work are in qualitative agreement with experimental observations and confirm the existence of dual mode transport which is central to the interpretation of the permselectivity in composite membranes systems.     

Silver(I) complexes of 9-anthracenecarboxylic acid and imidazoles: synthesis, structure and antimicrobial activity

[Ag(2)(9-aca)(2)] (1) (9-acaH = 9-anthracenecarboxylic acid) reacts with a series of imidazoles to give [Ag(imidH)(2.3)(CH(3)CN)(0.7)](9-aca) (3), [Ag(6)(imidH)(4)(9-aca)(6)(MeOH)(2)] (4), {[Ag(1-Me-imid)(2)](2)[Ag(4)(9-aca)(6)]} (5), {[Ag(1-Bu-imid)(2)](2)[Ag(4)(9-aca)(6)]} (6) and [Ag(apim)](9-aca)·H(2)O (7) (imidH = imidazole; 1-Me-imid = 1-methylimidazole; 1-Bu-imid = 1-butylimidazole; apim = 1-(3-aminopropyl)imidazole). The mononuclear complex 3, hexanuclear 4-6, and polymeric 7, were all characterised using X-ray crystallography. While many of the complexes possess excellent in vitro antifungal and antibacterial activities they are, unanimously, more effective against fungal cells. The insect, Galleria mellonella, can survive high doses of the Ag(i) complexes administered in vivo, and a number of the complexes offer significant protection to larvae infected with a lethal dose of pathogenic Candida albicans cells.     

Determination of the absolute configuration of [3(2)](1,4)barrelenophanedicarbonitrile using concerted time-dependent density functional theory calculations of optical rotation and electronic circular dichroism

The technique of time-dependent density functional theory (TDDFT) has very recently been applied to the calculation of both transparent spectral region optical rotations and electronic circular dichroism (CD). Here, we report the concerted application of the new methodologies to the determination of the absolute configuration (AC) of [3(2)](1,4)barrelenophanedicarbonitrile, 1, the first optically active barrelenophane. 1 is conformationally flexible: the two three-carbon bridges of 1 can each exhibit two conformations, leading to three inequivalent conformations of 1: a, b, and c. Conformational structures and energies are predicted using DFT at the B3LYP/6-31G level. Comparison of the calculated structures to structures obtained via X-ray crystallography of (+)-1 shows that (remarkably) all three conformations a-c are simultaneously present in crystalline (+)-1. The sodium D line specific rotations, [alpha](D), and CD spectra of a-c are calculated using TDDFT at the B3LYP/aug-cc-pVDZ level. Comparison of the conformationally averaged specific rotation and CD spectrum to the experimental data of Matsuda-Sentou and Shinmyozu leads to the AC 9S,12S(+)/9R,12R(-). The same AC is obtained both from [alpha](D) and from the CD, strongly supporting its reliability.