Luminescent lanthanide complexes with liquid crystalline properties

Lewis-base adducts of tris(β -diketonato)lanthanide(III) complexes were prepared, where the β -diketone is para -alkoxy-substituted 1,3-diphenyl-1,3-propanedione. These compounds are the first examples of liquid crystalline lanthanide complexes in which the mesomorphism is introduced via a β -diketonate ligand. Depending on the type of the Lewis base, the metallomesogens exhibit a monotropic smectic A or a monotropic highly ordered smectic phase. Intense photoluminescence was observed for the europium(III) complexes at room temperature.     

Time resolved fluorescence and anisotropy of 1-pyrene butyric acid and pyranine as probes of solvent organization in sucrose solutions

The microenvironment of solute-solvent interactions in aqueous sucrose solutions, ranging from 0 to 80 wt% in concentration, was investigated using time resolved fluorescence techniques. The fluorescence lifetimes and rotational correlation times of the trace fluorescent probes, PBA (1-pyrene butyric acid) and pyranine (trisodium 8-hydroxy-1,3,6-pyrenetrisulfonate), were measured in sucrose solutions. The behavior of the fluorescence lifetimes and the increase in the rotational correlation times with increasing sucrose concentration provided no evidence for the formation of water exclusive solute clusters in the metastable solutions. Instead, the results indicated the formation of a network of hydrogen bonding interactions between dispersed sucrose molecules.     

Mixed aqueous solutions as dilution media in the determination of residual solvents by static headspace gas chromatography

Static headspace (HS) sampling has been commonly used to test for volatile organic chemicals, usually referred to as residual solvents (RS) in pharmaceuticals. If the sample is not soluble in water, organic solvents are used. However, these seriously reduce the sensitivity in the determination of some RS. Here, mixed aqueous dilution media (a mixture of water and an organic solvent like dimethyl formamide, dimethyl sulfoxide or dimethyl acetamide) were studied as alternative media for static HS-gas chromatographic analysis. Although it has been known that mixed aqueous dilution media can often improve sensitivity for many RS, this study used a systematic approach to investigate phase volumes and the organic content in the HS sampling media. Reference solutions using 18 different class 1, 2 and 3 RS were evaluated. The effect of salt addition was also studied in this work. A significant increase in the peak area was observed for all RS using mixed aqueous dilution media, when compared with organic solvents alone. Matrix effects related to the mixed aqueous dilution media were also investigated and reported. Repeatability and linearity obtained with mixed aqueous dilution media were found to be similar to those observed with pure organic solvents.     

Local density of states and interface effects in semimetallic ErAs nanoparticles embedded in GaAs

The atomic and electronic structures of ErAs nanoparticles embedded within a GaAs matrix are examined via cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/XSTS). The local density of states (LDOS) exhibits a finite minimum at the Fermi level demonstrating that the nanoparticles remain semimetallic despite the predictions of previous models of quantum confinement in ErAs. We also use XSTS to measure changes in the LDOS across the ErAs/GaAs interface and propose that the interface atomic structure results in electronic states that prevent the opening of a band gap.     

Short-wave instabilities on a vortex pair of unequal strength circulation ratio

The creation of vortex pairs occurs in a range of industries, including mixing, transport, and plastic moulding. In particular, vortex pairs are observed in the wake of aircraft, and are the cause of a significant hazard in the aviation industry. Instabilities, which grow on vortex pairs, have the potential to lead to enhanced dissipation, thus limiting this safety concern, in addition to enhancing mixing in chemical engineering industries. To date research has mostly considered instabilities growing on a vortex pair where each vortex has the same magnitude of circulation. However, in practice it is unusual to have an equal-strength vortex pair. This investigation is the first to consider the instability modes that may develop on a Lamb–Oseen vortex pair of arbitrary circulation ratio. We find a significant change in the growth rates of all instability modes reported previously for an equal-strength vortex pair. All simulations employ an accurate spectral-element method to discretise the domain coupled with a three-step time splitting scheme. A wide range of instability wavelengths is considered to ensure that all instability modes are captured. By identifying and enhancing the leading instability modes, we are able to enhance the dissipation of the vortex pair.     

GrInvIn in a nutshell

GrInvIn (Graph Invariant Investigator) is a software framework for teaching graph theory and for research in graph theory and graph theoretic chemistry. It enables users to construct graphs, compute invariants (e.g. topological indices in chemistry) and investigate relations between these concepts. The design of GrInvIn emphasizes easy usage and makes use of software engineering techniques that enable the user to easily extend the system (e.g. by adding new topological indices to investigate).     

Measuring the primordial deuterium abundance during the cosmic dark ages

We discuss how measurements of fluctuations in the absorption of cosmic microwave background photons by neutral gas at redshifts z approximately 7-200 could reveal the primordial deuterium abundance of the Universe. The strength of the cross-correlation of brightness-temperature fluctuations in the redshifted 21-cm line of hydrogen with those in the redshifted 92-cm line of deuterium is proportional to the value of the deuterium-to-hydrogen ratio [D/H] fixed during big bang nucleosynthesis. Although challenging, this measurement would provide the cleanest possible determination of [D/H], free from contamination by structure formation processes at lower redshifts. We additionally report our result for the thermal spin-change cross section in deuterium-hydrogen scattering.     

Rimming flow of a power-law fluid: Qualitative analysis of the mathematical model and analytical solutions

Rimming flow of a non-Newtonian fluid on the inner surface of a horizontal rotating cylinder is investigated. Simple lubrication theory is applied since the Reynolds number is small and liquid film is thin. For the steady-state flow of a power-law fluid the mathematical model reduces to a simple algebraic equation regarding the thickness of the liquid film. The qualitative analysis of this equation is carried out and the existence of two possible solutions is rigorously proved. Based on this qualitative analysis, different regimes of the rimming flow are defined and analyzed analytically. For the particular case, when the flow index in a power-law constitutive equation is equal to 1/2, the problem reduces to the fourth order algebraic equation which is solved analytically by Ferrari method.     

Relics in medieval altarpieces? Combining X‐ray tomographic,laminographic and phase‐contrast imaging to visualize thin organic objects in paintings

X‐ray radiography is a common tool in the study of old master paintings. Transmission imaging can visualize hidden paint layers as well as the structure of the panel or canvas. In some medieval altarpieces, relics seem to have been imbedded in the wooden carrier of paintings. These are most probably thin organic fibrous materials such as paper or textile, which in traditional radiography are shadowed by the more absorbing surrounding material. This paper studies the application potential of synchrotron‐based tomographic and laminographic imaging complemented with phase‐contrast imaging for detection of such relics. The techniques are applied to a dummy painting. The results demonstrate that by using these imaging methods it is possible to three‐dimensionally visualize hidden cavities in panels and detect thin fibrous low‐Z materials sandwiched between a high‐Z paint layer and a thick wooden panel.