Dielectric Spectroscopy of Ferronematics Based on 6CHBT Liquid Crystal

In our study, the dielectric behaviour of the rod-like liquid crystal (6CHBT) doped with magnetic nanoparticles of spherical shape was investigated by means of dielectric spectroscopy in the frequency range from 20 Hz to 2 MHz. A low frequency dielectric dispersion in the nematic and isotropic phases of the pure liquid crystal (LC) has been assigned to the space charge polarization. After doping the host LC with the magnetic nano particles, a nearly Debye-like relaxation process was observed with the temperature dependence obeying the Arrhenius law. Considering a possible electric double layer formation on the particle surfaces, the detected relaxation process in the doped LC can be associated with the electric double layer polarization. The experimental results point out that in the measured frequency range the space charge and interfacial effects constitute the main dielectric response. Any anchoring effects were not observed and are therefore expected to appear in higher frequencies.     

Preparation and Regioselective Metalation of Bis(trimethylsilyl)methyl‐Substituted Aryl Derivatives

A range of bis(trimethylsilyl)methyl‐substituted aryl derivatives was prepared by using a Kumada–Corriu cross‐coupling reaction. The regioselective metalation of the resulting bis(trimethylsilyl)methyl‐substituted aryl derivatives bearing this bulky silyl group allowed the generation of functionalized aromatics. A regioselective switch in the presence or in the absence of the bis(trimethylsilyl)methyl group has been demonstrated. Furthermore, this silyl group was converted into a formyl group or a styryl group, enhancing the scope of application of such bis(trimethylsilyl)methyl‐substituted arenes.     

Ethylene Induction of Non-Enzymatic Metabolic Antioxidants in Matricaria chamomilla

Phytochemical investigations of Matricaria chamomilla L. (Asteraceae) stated the presence of several compounds with an established therapeutic and antioxidant potential. The chamomile non-enzymatic antioxidant system includes low molecular mass compounds, mainly polyphenols such as cinnamic, hydroxybenzoic and chlorogenic acids, flavonoids and coumarins. The objective of this work was to evaluate the role of the non-enzymatic antioxidant system after stimulation by ethylene in tetraploid chamomile plants. Seven days of ethylene treatment significantly increased the activity of phenylalanine ammonia-lyase, which influenced the biosynthesis of protective polyphenols in the first step of their biosynthetic pathway. Subsequently, considerable enhanced levels of phenolic metabolites with a substantial antioxidant effect (syringic, vanillic and caffeic acid, 1,5-dicaffeoylquinic acid, quercetin, luteolin, daphnin, and herniarin) were determined by HPLC-DAD-MS. The minimal information on the chlorogenic acids function in chamomile led to the isolation and identification of 5-O-feruloylquinic acid. It is accumulated during normal conditions, but after the excessive effect of abiotic stress, its level significantly decreases and levels of other caffeoylquinic acids enhance. Our results suggest that ethephon may act as a stimulant of the production of pharmaceutically important non-enzymatic antioxidants in chamomile leaves and thus, lead to an overall change in phytochemical content and therapeutic effects of chamomile plants, as well.     

Command surfaces, 20. Fixation of surface-assisted homogeneous alignment of nematic liquid crystals by cationic photopolymerization

The surface-assisted alignment of a nematic liquid crystal yields a persistent ordered structure upon cationic photopolymerization of liquid-crystalline epoxides. Linearly polarized light irradiation of a photocrosslinkable polymer containing azobenzene moieties played a crucial role in this procedure since the photoinduced alignment is not deteriorated by heating for polymerization.     

A Hypergeometric Inequality

A sequence of coefficients that appeared in the evaluation of a rational integral has been shown to be unimodal. The original proof is based on a inequality for hypergeometric functions. A generalization is presented.     

The purity of laboratory chemicals with regard to measurement uncertainty

The purity P of laboratory chemicals is often declared in the form P > or = xy% (e.g., P > or = 97%). With a randomly chosen set of 40 compounds we found that their purity is generally closer to 100% than to the lower limit. The distribution of the purity data as found in the laboratory depends on the analytical technique used. Whereas purities determined by chromatography do not exceed 100% (because the sum of all observed peak areas is set to 100%), the purities obtained by titration can exceed 100% (because the functionality of the compound is measured). Therefore, the data for these two groups need to be dealt with in different ways. For purities based on titration we propose to use a rectangular distribution with a range from Pmin to 101%, an expected purity value which is the mean and a standard uncertainty of the purity u(P) of 29% of the range. Purities determined by chromatography can be described with a triangular distribution (ramp function). One leg of the triangle represents the range from Pmin to 100% and the right-angle is located at 100%. The expected value is the median and the uncertainty u(P) is 24% of the range. These proposals match the experimental data well.     

Sharkovsky’s program for the classification of triangular maps is almost completed

For a continuous map of the interval, there are more than 50 conditions characterizing zero topological entropy. Some are applicable to the class of triangular maps (x,y)?(f(x),g_x(y)) of the square, but only a few of them are equivalent in this more general setting. In 1989, A.N. Sharkovsky posed the problem of proving or disproving all possible implications between them. During last 20 years, 32 conditions were considered, and most of the work was done. Only 45 relations out of 992 remained not clear. In this paper we give a survey of known results, provide two new examples disproving another 26 possible implications, and spell out the remaining 19 open problems; all but one concern distributional chaos.     

Macroporous antimony film electrodes for stripping analysis of trace heavy metals

We report on the elaboration of macroporous antimony film electrodes. The strategy to create macroporous electrodes is based on the replication of colloidal crystal templates. These electrodes of controlled porosity show an increased internal electroactive area and a significantly improved electrochemical performance. The application of this novel electrochemical sensor for the sensitive quantification of traces of heavy metals has been demonstrated in combination with differential pulse anodic stripping voltammetry in model solutions.