Improvement of electrical conductivity of silicon nitride/carbon nano-fibers composite using magnesium silicon nitride and ytterbium oxide as sintering additives

In order to find out the influence of sintering additives on the electrical conductivity of Si₃N₄-based ceramics composites with dispersed carbon nano-fibers (CNFs) two different mixtures of sintering additives were tested – Al₂O₃/Yb₂O₃ and MgSiN₂/Yb₂O₃, respectively. Optimization of hot-pressing conditions was performed for each mixture. The results show that the electrical conductivity can be effectively increased up to 1315 S/m by replacement of traditional sintering aid – alumina, with magnesium silicon nitride, while the mechanical properties remained on the same level. Other advantages of using MgSiN₂ instead of alumina are the preservation of higher amounts of CNFs in the ceramic composite and lower densification temperature (1500 °C) compared to samples sintered with alumina-based sintering aids (1550 °C).     

Technical Note — Analysis of Beer Aroma Compounds by Solid‐phase Microcolumn Extraction

Due to their low dead volumes, microcolumns with Tenax TA coupled to a capillary column in the modified GC inlet allow analysis of a broad range of compounds (from acetaldehyde to 2‐phenylethanol) in a single sample run. In this study, a micro‐column was filled with 10 mg of Tenax TA. Chromatograms showed well‐resolved peaks even at the beginning of the run. Static headspace was used to pre‐concentrate the compounds. The method is rapid, simple and inexpensive.     

Information and communication theory in molecular biology

The DNA sequencing efforts of the past years together with rapid progress in sequencing technology have generated a huge amount of sequence data available in public molecular databases. This recent development makes it statistically feasible to apply universal concepts from Shannon’s information theory to problems in molecular biology, e.g to use mutual information for gene mapping and phylogenetic classification. Additionally, the genetic information in the cell is continuously subject to mutations. However, it has to be passed from generation to generation with high fidelity, raising the question of existence of error protection and correction mechanisms similar to those used in technical communication systems. Finally, better understanding of genetic information processing on the molecular level in the cell can be acquired by looking for parallels to well established models in communication theory, e.g. there exist analogies between gene expression and frame synchronization.     

Modification of lignin–polyethylene blends with high lignin content using ethylene–vinylacetate copolymer as modifier

Blending of polyethylene with lignin in concentrations > 20 wt % yielded blends with relatively low mechanical properties. A new method, based on modification of polyethylene with ethylene–vinylacetate (EVA) copolymer, was developed for the preparation of polyethylene blends containing about 30 wt % lignin with acceptable strength properties. The addition of 10 wt % EVA caused an increase of tensile strength about twice and elongation at break about 13 times compared to those of the corresponding nonmodified samples. The optimization of lignin–polyethylene–EVA blend composition was based on a regression equation, which was obtained as output from an experimental design. The prepared composite material with 33.6 wt % lignin showed acceptable processing and mechanical properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1855–1860, 2004     

Preceramic Polymer‐Derived SiAlON as Sintering Aid for Silicon Nitride

Two kinds of sintering additives based on the polysiloxanes or polysilazanes filled with nano‐sized powders as SiAlON precursors were tested for the densification of Si₃N₄‐based ceramics. The results showed that both systems can be successfully used as additives for the preparation of Si₃N₄ ceramics with favorable mechanical characteristics. The ceramics were sintered with 18 wt% of preceramic polymer‐based mixture, and good fracture resistance and high hardness values were obtained after sintering in optimized conditions (temperature, dwell time, nitrogen pressure). Higher densification temperatures and longer holding times were required for sintering of samples with polysilazane‐based precursors. The best toughness values were approximately 5 MPa·m^0.5, while the highest hardness was about 19 GPa. The differences in mechanical properties of the prepared composites can be related to the phase composition, microstructure and different chemical bonds present in the ceramic residue generated upon pyrolysis and final densification.     

Surface and porous recast layer analysis in µ-EDM of MWCNT-Al2O3 composites

Machining of ceramic materials has been a major challenge owing to high hardness and brittleness. The reinforcement of a conducting filler allows permissible machining in electrical discharge machining (EDM) process. The current effort analyses the impact of multi-walled carbon nanotubes (MWCNT) of concentrations of 2.5 and 5 vol. %, as conducting filler towards machinability of alumina composites in µ-EDM process. The influence of tool materials and its rotation are closely analyzed. A successful machining process is observed in both the two composites, with a higher material removal rate (MRR) in 5 vol. % MWCNTs. When the tool starts to rotate at 750 rpm, an increment of around 60–65% is observed in MRR for both the two composites. Similarly, the surface roughness (R_a) decreases by a factor of 20?25%. The brass tool is observed to yield better machining capabilities due to the frequent initiation of sparks. A highly porous machined surface is observed in both the two composites. This scenario depicts the spalling effect as more dominant than melting-evaporation effect. The extent of porous recast layer on the drilled edges is found to reduce with increasing the speed of tool rotation.     

Choquet integral with respect to ?ukasiewicz filters, and its modifications

In many decision problems a set of actions is evaluated with respect to a set of points of view, called criteria. This paper follows two aims - first to compare the so-called level-dependent Choquet integral introduced recently by Greco et al. with another transformation of Choquet integral, proposed by Havranová and Kalina. The other aim of this paper is to look for an appropriate utility function in a given setting. We illustrate our approach on a practical example, utilizing the level-dependent Choquet integral.     

A time-space tradeoff for language recognition

We define a languageL and show that its time and space complexitiesT andS must satisfyT ² S cn ³ even allowing machines with multiple (non random) access to the input.The second author was supported in part by the Israel Commission for Basic Research.     

Nanoindentation and tribology of a (Hf-Ta-Zr-Nb-Ti)C high-entropy carbide

A (Hf-Ta-Zr-Nb-Ti)C high-entropy carbide was prepared by ball milling and a two-step Spark Plasma Sintering process, achieving a single-phase ceramic sample with a high relative density of 99.4 %. The wear resistance of the sample was measured by tribology and micro-scale mechanical behaviour was studied by nanoindentation on both the non-deformed and worn surfaces. Grains and the vicinity of grain boundaries exhibited high hardness values of 38.5 ± 0.5 GPa and 35.5 ± 1.0 GPa with similar Young’s moduli of 562 ± 11 GPa and 547 ± 16 GPa, respectively. The dominant wear mechanism was mechanical wear with limited grain pull-out and fracture, and with a localized and thin tribo-layer formation. The specific wear rate exhibited an increase with the increasing load from 2.53·10^?6 mm³/Nm at 5 N to 9.03·10^?6 mm³/Nm at 50 N. This was correlated to the decrease of nanohardness of the worn surfaces with increasing wear load, which is attributed to the increased number of microcracks.