The influence of dopants on loss tangent of polycrystalline alumina ceramics

Polycrystalline aluminas with various concentrations of oxide dopants CaO, MgO, and TiO₂, ranging from 0.05 wt.% to 5 wt.%, as well as pure alumina references were prepared by slip casting from suspensions with various solid loading (30, 35, and 40 vol.% of Al₂O₃), and sintered at 1350 °C for 1 h as low loss tangent electroceramics. As the key parameter for intended application the loss tangents were measured at room temperature in the frequency range between 1 and 200 kHz. In the case of pure alumina the lowest value of loss tangent was achieved in the materials with minimum residual porosity. The values of loss tangents of doped materials were influenced by the concentration of dopants. The addition of 0.05 and 0.5 wt.% of MgO and CaO decreased the value of loss tangent in the whole frequency range. The effect was related to more homogenous microstructure with lower concentration of defects (pores) resulting from the addition of dopants. The increased values of loss tangent in the materials with higher level of additives (5 wt.%) are related to lower density of the materials, and the presence of residual porosity. Other contributing factors are the formation of secondary phases (calcium, magnesium and titanium aluminates), and the increased concentration of lattice defects due to incorporation of atoms with different valencies to alumina crystal lattice.     

Utilization of laser‐assisted analytical methods for monitoring of lead and nutrition elements distribution in fresh and dried Capsicum annuum l. leaves

Laser induced breakdown spectroscopy (LIBS) and laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) have been applied for high‐resolution mapping of accumulation and distribution of heavy metal (lead) and nutrition elements (potassium, manganese) in leaves of Capsicum annuum L. samples. Lead was added in a form of Pb(NO₃)₂ at concentration up to 10 mmol L^?1 into the vessels that contained tap water and where the 2‐months old Capsicum annuum L. plants were grown another seven days. Two dimensional maps of the elements are presented for both laser‐assisted analytical methods. Elemental mapping performed on fresh (frozen) and dried Capsicum annuum L. leaves are compared. Microsc. Res. Tech., 2011. © 2010 Wiley‐Liss, Inc.     

The comparison of structure and properties in DC magnetron sputtered and HiPIMS W-C:H coatings with different hydrogen content

The comparison of the structure, composition, hardness and friction behavior of DCMS and HiPIMS W-C:H coatings made by hybrid reactive deposition in the presence of C₂H₂ and H₂ in Ar atmosphere revealed a transition from textured to columnar-like structures with the increased addition of acetylene in DCMS coatings whereas only amorphous-like structures were produced by HiPIMS. The hybrid sputtering involves acetylene and hydrogen dissociation and recombination reactions in the plasma resulting in the generation of carbon as well as –CH₃ and =CH₂ radicals which are chemisorbed at the growing coating surface. The concentration of hydrogen in carbon matrix seems to be controlled by –CH₃ and =CH₂ radicals and not by the amount of molecular hydrogen. The main advantage of HiPIMS compared to DCMS technology includes coefficients of dry friction below 0.1 attributed to the formation of lubricious transfer layer at moderate level of hardness (around 20?GPa) over the studied acetylene additions range. Hybrid HiPIMS technology seems to offer possibilities for substantial COF decrease without hardness degradation which results in widening of the potential of W-C:H coatings for practical engineering applications.     

A new high-molecular-weight glutenin subunit from the slovak wheat (Triticum aestivum L.) cultivar ‘Trebišovská 76’

Historical and local varieties are an important source of genetic diversity in connection with the wheat baking quality. By analysis of DNA from the coding part of the genome of the Slovak regional wheat (Triticum aestivum L.) variety ‘Trebišovská 76’, differences in the Dy subunit composition coded by locus Glu-1D were found. Comparing the newly found sequence with a generally used 1Dy12 (GenBank accession no. X03041) sequence, existence of a new high-molecular-weight glutenin subunit, which was marked as 1Dy12* (GenBank accession no. EU266533) was confirmed. The molecular weight of probable protein coded by 1Dy12* subunit reaches 72.35 kDa comparing to the 1Dy12, which reaches 68.71 kDa. This difference is not likely to distinguish by SDS-PAGE. The easiest way for cereal genotyping according to baking quality is proteomic analysis. More exact and suitable method for genotype identification appears to be marker assisted selection using PCR.

     

Solid Acids as Heterogeneous Support for Primary Amino Acid‐Derived Diamines in Direct Asymmetric Aldol Reactions

We have achieved the non‐covalent immobilization of chiral primary amino acid‐derived diamines on organic and inorganic sulfonated solid acids through acid‐base interaction. With the commercial sulfonated fluoropolymer nafion® NR50 as support an optimal balance was found between activity and stereoselectivity of the supported catalyst in direct asymmetric aldol reactions of linear ketones and aromatic aldehydes. Under optimized conditions aldol products were obtained in high yields and with excellent enantioselectivities for the syn‐product (up to 98% ee). Furthermore, catalysis with the supported diamine was demonstrated to occur truly heterogeneously and the loaded nafion® NR50 beads could be reused several times. Ultimately, the immobilized catalyst/nafion® NR50 system was successfully implemented in a fixed‐bed reactor set‐up under continuous flow conditions.     

Field oscillations in a micromaser with injected atomic coherence

Abstract

The electric field in a lossless, regularly-pumped micromaser with injected atomic coherence can undergo a period-two oscillation in the steady state. The field changes its value after a single atom passes through the micromaser cavity, but returns to its original value after a second atom travels through. We give a simple explanation for this phenomenon in terms of tangent and cotangent states. We also examine the effect of cavity damping on this steady state.     

Determination of Ketchup Sensory Texture Acceptability and Examination of Determining Factors as a Basis for Product Optimization

The aim of this study was to examine possible usage of instrumental determination of selected texture parameters to estimate sensory texture acceptability of ketchups. Likewise, the authors focused on examination whether the consumer’s perception of texture acceptability is connected to the selected factors related to the ingredients and production technology. Yet another aim was to describe the selected textural parameters of ketchups available in the European market. Within the frame of this study, 29 samples of ketchups were analyzed by means of instrumental and sensory texture analysis. Further, a survey research was carried out with the results showing that the texture was the second most significant parameter for the consumer’s choice of a particular product. The average evaluation of sensory texture acceptability reached the values from 3.78 to 7.67. Analysis of the evaluation results of textural parameters based on the values of Pearson’s correlation coefficient confirmed a high correlation (p < 0.05) between instrumental and sensory determined viscosity and density. However, none of these partial textural parameters affected the sensory acceptability of the texture separately. Thus, using the instrumental analysis for estimation of the sensory texture acceptability of ketchups is not possible. For the optimization and control of ketchup texture in practice, sensory analysis is essential.     

Heterogeneous Catalysts for Racemization and Dynamic Kinetic Resolution of Amines and Secondary Alcohols

This paper gives an overview of the available heterogeneous catalysts for racemization of chirally stable secondary alcohols and amines, and of the combination of these catalysts with immobilized enzymes in dynamic kinetic resolution (DKR) for production of enantiopure esters or amides. For the one-pot DKR process, compatibility of enzyme and heterogeneous catalyst is a major issue, and in some cases the combination fails because of (mutual) deactivation. Heterogeneous catalysts of various types, such as zeolites or oxides effect alcohol racemization; they function either via acid catalysis and carbenium chemistry, or via a redox pathway via the ketone. Dynamic kinetic resolution of aliphatic alcohols using a heterogeneous catalyst in mild conditions is however an open challenge. Heterogeneous amine racemization catalysts invariably operate using a redox mechanism via the imine. In this case, the scope encompasses benzylic and aliphatic amines. The practicality of the approach is illustrated with the production of enantiopure N-acylated homoserine lactones, which are signalling compounds in microbial communities.