Aliphatic polycarbonate‐based polyurethane elastomers and nanocomposites. I. The influence of hard‐segment content and macrodiol‐constitution on bottom‐up self‐assembly

Aliphatic polycarbonate‐based polyurethane (PC‐PU) elastomers as well as their nanocomposites with organic‐modified clay (bentonite for organic system) were synthesized. Macrodiols (MD) (randomly copolymerized aliphatic PC‐glycols of molecular weight of about 2000: T5652, T4672, and T4692), hexamethylene diisocyanate, and butane‐1,4‐diol were used as starting materials. Solid‐state NMR and Fourier transform infrared spectroscopy, small‐angle X‐ray scattering, wide‐angle X‐ray diffraction, atomic force microscopy, and transmission electron microscopy were used for studying the bottom‐up self‐assembly of building units from the segmental level up that of organized structures of micrometer sizes. Contents of hard segments formed by the reaction of chain extender with diisocyanate plays a dominant role for the degree of ordering and related phenomena, while the MD chain has only limited effect on PC‐PU properties. The spectroscopy and scattering experiments suggest that bentonite particles incorporate well in the structure and promote the ordering of hard segment domains in PC‐PU matrix as compared with the nanofiller‐free analogue. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Novel Approaches in Mathematical Description of Hen Egg Geometry

Precise quantification of the profile of a hen egg can provide a powerful tool for analysis of egg shape and following solving of various technological problems. The article presents a new approach of the eggshell geometry determination using and analyzing the egg digital image and edge detection techniques. The detected points on the eggshell contour were fitted by the Fourier series. The obtained equations describing an egg profile were used to calculate the egg volume, surface area, and radius of curvature with a much higher degree of precision in comparison with previously published approaches. It was shown that radii of curvature at the critical points of the egg profile are independent on the egg shape index. The article shows and quantifies the limitations of the common and frequent procedures.     

The role of oleate-functionalized layered double hydroxide in the melt compounding of polypropylene nanocomposites

In this research, the oleate-functionalized magnesium and aluminum layered double hydroxide (LDH; Mg:Al = 3:1) o-LDH was applied as nanofiller in the melt blending of polypropylene (PP) nanocomposites, in order to understand its role in this process. o-LDH was prepared using the memory effect of the calcined carbonated LDH. Blending of PP and low o-LDH filler contents of 0.45 and 0.90 wt.% afforded the nanocomposites PP0.45 and PP0.90, respectively, which were characterized by transmission electron microscopy, X-ray diffraction, small angle X-ray scattering, thermo-gravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis. The oleate LDH surface functionalization enhanced the system compatibility as a relative regular dispersion of o-LDH tactoids was observed within the matrix, together with partial PP intercalation. This o-LDH incorporation increased the PP relative crystallinity, induced crystalline orientation and decreased the glass transition temperature. Furthermore, the nanocomposites showed improved initial resistance to decomposition and stiffness. These results showed that the o-LDH acted as both nucleating agent and plasticizer, and that the presented approach can be used for the development of PP nanocomposites with distinguished properties.     

Configurable front-end converters for multicurrent locomotives operated on 16 2/3 Hz AC and 3 kV DC systems

A configurable converter topology is presented as front-end converter for a locomotive that can be operated as well on a high voltage AC-system as on a medium voltage DC-system. The configurable converter is realized on the base of a multilevel chain, where all modules are fed through reversible and isolated DC-DC stages. The medium frequency transformers used in the isolation stages of the DC-DC converters allow a significant weight reduction of the locomotive, in comparison with the classical low-frequency voltage-transformers. A first solution using hard switching techniques is presented, using a three-times silicon-conversion. A second solution based on ZVT/ZCS techniques is then presented, with the advantage of having ideally only a two times silicon conduction. Prototype modules have been realized with association of diodes and IGBTs in order to provide reverse-blocking devices. First results of the two-stage conversion are also presented.     

Telomere length dynamics in human lymphocyte subpopulations measured by flow cytometry

To measure the average length of telomere repeats at chromosome ends in individual cells we developed a flow cytometry method using fluorescence in situ hybridization (flow FISH) with labeled peptide nucleic acid (PNA) probes. Results of flow FISH measurements correlated with results of conventional telomere length measurements by Southern blot analysis (R = 0.9). Consistent differences in telomere length in CD8+ T-cell subsets were identified. Naive and memory CD4+ T lymphocytes in normal adults differed by around 2.5 kb in telomere length, in agreement with known replicative shortening of telomeres in lymphocytes in vivo. T-cell clones grown in vitro showed stabilization of telomere length after an initial decline and rare clones capable of growing beyond 100 population doublings showed variable telomere length. These results show that flow FISH can be used to measure specific nucleotide repeat sequences in single cells and indicate that the very large replicative potential of lymphocytes is only indirectly related to telomere length.     

A three-phase multilevel converter for high-power induction motors

A new converter topology for drives is presented in this paper: a three-phase multilevel converter with separately regulated DC power supplies. The DC voltages are provided by medium-frequency DC-DC converters. The applications for the converter are especially high-power traction systems, where the voltage applied to the induction motor is bigger than 1 kV. The motor current is of a very high quality, compared to a classical three-phase converter. This allows keeping the switching frequency low by using phase-shifted pulsewidth modulation (PWM) carriers. Different modulation methods have been developed and simulated. Experimental tests have been made on a 12 kW prototype     

Effect of nanofiller on the behavior of a melt‐drawn HDPE/PA6 microfibrillar composite

Microfibrillar composites (MFCs) with reinforcing fibrils formed in situ by melt drawing were modified by the addition of layered silicates using different mixing protocols, viz simultaneous addition of components, application of respective premade nanocomposites and their combinations. The objective was to combine reinforcement with changes in the final structure, especially the fibril dimensions. The presented results indicate good potential of the nanoclay to enhance the MFC based on the melt‐drawn HDPE/PA6 system. The best mechanical behavior was achieved with the simultaneous addition of all components. The majority of the nanofiller material was contained inside the PA6 fibrils. Both fibrils dimensions and mechanical behavior were significantly affected by the nanofiller migration to the PA6 phase in the course of mixing and melt drawing. Due to a complex effect of the clay, deterioration of mechanical properties was also found. As a result, numerous, in some cases contradictory, effects of nanofillers must be perfectly harmonized to improve the properties of MFCs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41868.