A theoretical analysis of scattering loss from planar optical waveguides

We derive analytical expressions for the scattering loss in planar optical waveguides whose surface roughness can be described by an exponential or Gaussian autocorrelation function. Our results show, for the first time, the explicit dependence of the loss coefficient on all the waveguide parameters. In addition, we show that for any waveguide there is a simple upper limit for the scattering loss.     

Liquid-crystalline polysiloxanes with fluoro-substituted side chains

Sixteen new side chain liquid polysiloxanes, either homopolymers derived from poly(hydrogenmethyl)siloxane or copolymers derived from poly(hydrogenmethyl-dimethylsiloxane), are reported with side chains carrying fluoro-substituents. The known effects of fluoro-substitution in low molar mass liquid crystals are strongly echoed in the polymeric analogues and interesting comparisons are made between homo- and co-polymers carrying the same fluorinated side chains.     

Synthesis and characterization of a range of heterocyclic liquid crystalline materials incorporating the novel thiophene-pyrimidine moiety

In this structure/property study six 2-(4-alkyloxyphenyl)-5-thiophen-2-ylpyrimidines and thirty-six 2-(4-alkyloxyphenyl)-5-(5-alkylthiophen-2-yl) pyrimidines were synthesized to evaluate the effect of the introduction of heterocyclic rings on the liquid crystalline (LC) behaviour of mesogens. The 'bent' nature of the structure of the 2-(4-alkyloxyphenyl)-5-thiophen-2-yl-pyrimidines, due to the presence of the thiophene ring, was further exaggerated in the 2-(4-alkyloxyphenyl)-5-(5-alkylthiophen-2-yl) pyrimidines by the incorporation of an alkyl group at the 5-position in the thiophene ring. This simple change in structure led to a remarkable change in the LC behaviour of the mesogens. From a series of mesogens having high melting points and exhibiting monotropic nematic phases, the incorporation of the alkyl group gave a series of three-ring mesogens with relatively low melting points (60-80°C), and exhibiting a range of tilted smectic phases, including SmI, SmC and SmC alt phases.     

A relationship between dielectric permittivity of the nematic continuous phase material and the shear stresses of electro-rheological fluids containing liquid crystalline materials

Further investigations into the behaviour of electro-rheological fluids containing liquid crystalline materials have been made. Dramatic changes in the shear stresses of such suspensions have been observed around the temperature at which the liquid crystalline component undergoes a change of phase from the nematic to the isotropic phase. The temperature profile of shear stress is predicted to be mirrored by that of the mean dielectric permittivity of the liquid crystalline component in the electro-rheological fluid.     

Synthesis and evaluation of a series of novel 2-substituted poly(allylalcohol) side chain liquid crystalline oligomers exhibiting ferroelectricity

The recently published Baylis-Hillman methodology has been used to prepare a number of side chain liquid crystalline poly(allylalcohols) incorporating a ferroelectric mesogenic side chain. These poly(allylalcohols) exhibited wide range S*_C phases and, in the case of two of these materials, low glass transition temperatures. The transition temperatures and phase behaviour of the SCLC poly(allylalcohols) were compared to acrylate and methacrylate SCLC oligomers containing a similar mesogenic side chain. The response times for two poly(allylalcohols) exhibiting low glass transition temperatures were also measured over a wide temperature range. Although the poly(allylalcohols) had comparable response times to the analogous acrylate and methacrylate SCLCP, they showed the greater temperature dependence of the response time. However, at 39°C one of the SCLC poly(allylalcohols) showed a response time of 65 ms.     

Preliminary investigation of fungal bioprocessing of wheat straw for production of straw-thermoplastic composites

Straw utilization for composites is limited by poor resin and polymer penetration, and excessive resin consumption owing to the straw cuticle, fines, and lignin-hemicellulose matrix. White-rot fungi degrade these components of straw and could, therefore, potentially be used to improve resin penetration and resin binding without the use of physical or chemical pretreatments. Although long treatment times and large footprints the limit use of fungal treatments on a large scale, distributed fungal pretreatments could alleviate land requirements. In this article, we present progress toward the development of a passive fungal straw upgrading system utilizing whiterot fungi.     

On the disappearance of criticality in the theory of thermal ignition

A recent article by K. K. Tam in this journal stated results on the values of the activation energy for which a nonlinear eigenvalue problem, which arises in the steady-state theory of thermal ignition, has multiple solutions. This report points to an error contained therein and gives the corrected values of the activation energy for which multiplicity occurs.

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Zusammenfassung Eine vor kurzem erschienene Arbeit in dieser Zeitschrift von K. K. Tam stellte Ergebnisse für die Werte der Aktivierungsenergie fest, für die ein nichtlineares Eigenwert-Problem, das in der stationären Theorie der thermischen Zündung entsteht, vielfache Lösungen hat. Dieser Bericht weist auf einen darin enthaltenen Fehler hin und gibt die korrigierten Werte der Aktivierungsenergie, für die es vielfache Lösungen gibt.

     

Plasmonic Surfaces for Cell Growth and Retrieval Triggered by Near‐Infrared Light

Methods for efficient detachment of cells avoiding damage are required in tissue engineering and regenerative medicine. We introduce a bottom–up approach to build plasmonic substrates using micellar block copolymer nanolithography to generate a 2D array of Au seeds, followed by chemical growth leading to anisotropic nanoparticles. The resulting plasmonic substrates show a broad plasmon band covering a wide part of the visible and near‐infrared (NIR) spectral ranges. Both human and murine cells were successfully grown on the substrates. A simple functionalization step of the plasmonic substrates with the cyclic arginylglycylaspartic acid (c‐RGD) peptide allowed us to tune the morphology of integrin‐rich human umbilical vein endothelial cells (HUVEC). Subsequent irradiation with a NIR laser led to highly efficient detachment of the cells with cell viability confirmed using the MTT assay. We thus propose the use of such plasmonic substrates for cell growth and controlled detachment using remote near‐IR irradiation, as a general method for cell culture in biomedical applications.     

On the open-circuit interaction between methanol and oxidized platinum electrodes

In the present work, results of the interaction between methanol and oxidized platinum surfaces as studied via transients of open-circuit potentials are presented. The surface oxidation before the exposure to interaction with 0.5 M methanol was performed at different polarization times at 1.4 V vs reversible hydrogen electrode (RHE). In spite of the small changes in the initial oxide content, the increase of the pre-polarization time induces a considerable increase of the time needed for the oxide consumption during its interaction with methanol. The influence of the identity of the chemisorbing anion on the transients was also investigated in the following media: 0.1 M HClO₄, 0.5 M H₂SO₄, and 0.5 M H₂SO₄ + 0.1 mM Cl⁻. It was observed that the transient time increases with the energy of anion chemisorption and, more importantly, without a change in the shape of the transient, meaning that free platinum sites are available at the topmost layer all over the transient and not only in the potential region of small oxide ‘coverage’. The impact of the pre-polarization time and the effect of anion chemisorption on the transients are rationalized in terms of the presence of surface and subsurface oxygen driven by place exchange.