Mechanically activated cholesteric polymer dispersed liquid crystals

In this paper we deal with a cellulose derivative cholesteric dispersed liquid crystal (CCDLC) with mechanically tuneable optical properties. The composite is formed with a matrix of acetoxypropylcellulose with embedded micrometric and submicrometric droplets of a cholesteric mixture. Polarizing optical microscopy and atomic force microscopy (AFM) measurements performed on the system are reported and it is shown that the wavelength of the reflected light can be changed by a temperature variation and it is also changeable through a mechanical deformation. The pitch of the deformed droplets can be measured from AFM photographs and compared with the wavelength reflected by the CCDLC composite material.     

New polytope decompositions and Euler-Maclaurin formulas for simple integral polytopes

We give new weighted decompositions for simple polytopes, generalizing previous results of Lawrence-Varchenko and Brianchon-Gram. We start with Witten's non-abelian localization principle in equivariant cohomology for the norm-square of the moment map in the context of toric varieties to obtain a decomposition for Delzant polytopes. Then, by a purely combinatorial argument, we show that this formula holds for any simple polytope. As an application, we study Euler-Maclaurin formulas.     

Study of the effects of unsupervised over‐the counter whitening products on dental enamel using μ‐Raman and μ‐EDXRF spectroscopies

The purpose of this in vitro study was to assess whether the mineralization degree and elemental content in tooth enamel are altered when bleaching the teeth with two different over‐the‐counter bleaching gels, exceeding the recommendations of the manufacturer. In order to perform this evaluation, 12 healthy teeth were used, six samples were treated with Teeth Whitening Home Kit, and the other six samples were treated with WHITE! (Bingo‐UK) bought in online shopping sites, for the period of 39 days. The pH of each product and the elemental content of each sample, before and after, were obtained by energy dispersive X‐ray spectrometry and phosphate (PO₄^3‐) profile was evaluated with Raman spectroscopy. Data was analyzed accordingly to a pre‐established plan with a mixed‐model ANOVA for repeated measures, significance was set at 5%. Both products were markedly acidic and below enamel critical level of 5.5. Moreover, seven days after treatment, demineralization was significant, wherein at the end of the study the degree of demineralization seems to be permanent. Copyright © 2015 John Wiley & Sons, Ltd.     

Anisotropic cellulose-derived matrix for dispersed liquid crystals

New cellulose-derived dispersed liquid crystal free-standing thin films were prepared by a shear-casting technique from anisotropic and isotropic solutions of thermotropic (acetoxypropyl)cellulose in N,N-dimethylacetamide with different amounts of the nematic E7. For films prepared from anisotropic solutions, dispersed nematic E7 droplets of micron and submicron size were found to coexist, with the band texture characteristic of polymer liquid crystals after shearing. Mechanical properties including Young's modulus and stress-strain curves were determined along and perpendicular to the shear direction, and revealed the anisotropic behaviour of films prepared from lyotropic solutions. The nematic E7 component appears to promote chain mobility and rearrangement of the polymer matrix and to modify the viscoelastic properties of the matrix.     

Novel triterpenoids from the fungus Pisolithus tinctorius

The structures of two triterpenes, possessing novel side chains, were elucidated by chemical correlations with known compounds and physical methods involving in particular nuclear overhauser effect difference spectroscopy.     

Preparation and liquid-crystalline properties of toluene-4-sulphonyl urethane of hydroxypropylcellulose

A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) of M_w = 60000 g mol^-1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone and N,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase.     

A new spot test for fluoride

Summary Solution of silver ion, which is stable in the presence of appropriate concentrations of ferrous and ferric salts, is reduced by ferrous salts if fluoride is added. This fact has been utilized to develop a spot test for fluoride. 2g of fluoride ion can be detected. A method for the removal of fluoride from interfering ions is also described.

---

Zusammenfassung Silberlösungen, die in bestimmten Konzentrationen von Eisen(II)- und Eisen(III)-salzen beständig sind, werden von Eisen(II)-salzen reduziert, wenn man Fluorid zusetzt. Auf dieser Grundlage wurde eine Tüpfelreaktion für Fluorid ausgearbeitet. 2 g F^– können damit nachgewiesen werden. Eine Methode zur Abtrennung von Fluorid von störenden Ionen wurde ebenfalls angegeben.

     

On the diophantine equation v(v+1)=u(u+a)(u+2a)

Let \(a\in \mathbb {N}\) . We discuss the diophantine equation $$v(v+1)=u(u+a)(u+2a) $$ and some important arithmetic properties of the associated cubic field. We also present a detailed account of the cases a=2 and a=5.     

Prediction of airborne sound and impact sound insulation provided by single and multilayer systems using analytical expressions

In this work, the authors use analytical solutions to assess the airborne sound and impact insulation provided by homogeneous partitions that are infinite along their plane. The algorithm uses Green’s functions, derived on the basis of previous work by the authors on the prediction of airborne sound insulation provided by single and double panels. The model is now extended to handle multilayer systems, allowing the simulation of three-dimensional loads applied in both the acoustic and solid media.The model is validated against experimental results and compared with simplified expressions for single, double and triple panels. The results provided by the analytical model were found to provide a good agreement with the experimental results, except in the vicinity of the coincidence effect in the presence of thicker panels.The applicability of the proposed tool is then illustrated by analyzing the acoustic behavior provided by single layers and by a suspended ceiling. Different variables are studied, such as the mass, the stiffness of the layers, the position and direction of the load within the elastic medium and the presence of porous material in the fluid layers. It was found that the model is able to simulate the acoustic phenomena involved in single and multilayer systems.