Comb-like thermoresponsive polymeric materials: Synthesis and effect of macromolecular structure on solution properties

A series of comb-like block and random copolymers based on acrylamide (AM) and N-isopropylacrylamide (NIPAM) have been prepared by atom transfer radical polymerization (ATRP). The number of side-arms, the length of the AM and NIPAM blocks as well as the distribution of the two monomers (block or random) were systematically varied. The aqueous solution properties, i.e. the solution viscosity as a function of shear rate and temperature and the critical micelle concentration (CMC) of the different copolymers were evaluated. Particular emphasis is dedicated to the thermo-responsiveness of the aqueous copolymer solutions as measured by the rheological behaviour. The CMC is a function of the molar ratio between the AM and NIPAM, as well as the distribution (block or random). The surface tension of the block copolymers is close to the value for pure poly(NIPAM), while that of the random copolymers is a function of the composition. The block copolymers tend to precipitate from the solution at temperatures above the Lower Critical Solution Temperature (LCST) of poly(NIPAM), indicating the formation of strong aggregates. Random copolymers of AM and NIPAM do not precipitate from the solution (up to 80 °C). In addition, depending on the composition, thermothickening behaviour is observed. The thermothickening behaviour is only present at low shear rates (γ ≤ 10 s⁻¹). This, in connection with the ease of the synthesis, makes these copolymers especially interesting for application in Enhanced Oil Recovery (EOR).     

X-ray based tools for the investigation of buried interfaces in organic electronic devices

X-ray reflectivity combined with grazing incidence diffraction is a valuable tool for investigating organic multilayer structures that can be used in devices. We focus on a bilayer stack consisting of two materials (poly-(3-hexylthiophene)) (P3HT) and poly-(4-styrenesulfonic acid) (PSSA) spin cast from orthogonal solvents (water in the case of PSSA and chloroform or toluene for P3HT). X-ray reflectivity is used to determine the thickness of all layers as well as the roughness of the organic–organic hetero-interface and the P3HT surface. The surface roughness is found to be consistent with the results of atomic force microscopy measurements. For the roughness of P3HT/PSSA interface, we observe a strong dependence on the solvent used for P3HT deposition. The solvent also strongly impacts the texturing of the P3HT crystallites as revealed by grazing incidence diffraction. When applying the various PSSA/P3HT multilayers in organic thin-film transistors, we find an excellent correlation between the determined interface morphology, structure and the device performance.     

Vaporization and Corrosion of Refractories in the Presence of Pressurized Pulverized Coal Combustion Slag

The corrosion and vaporization behavior of eight commercial refractories containing Cr₂O₃ were investigated under simulated pressurized pulverized coal combustion (PPCC) conditions at 1723 K in the presence of liquid slag. The corrosion resistance of the refractory materials decreased with increased content of free Cr₂O₃, because bursting (reaction of Fe₃O₄ with Cr₂O₃) occurred. Refractories containing MgCr₂O₄ with dissolved Al₂O₃ showed the highest corrosion resistance. Thermodynamic calculations showed that CrO₃ and CrO₂(OH)₂ were the most volatile species in air and in PPCC flue gas, whereas additions of A₂O (A = Na and K, minor slag component) increased the chromium vaporization significantly because of A₂CrO₄ formation. Knudsen effusion mass spectrometry measurements showed that the chromium vaporization of refractories was directly correlated to the Cr₂O₃ content of the material. In contrast, refractories containing MgCr₂O₄ showed a significant decrease in chromium vaporization.     

Production and Electrostatic Precipitation of Combustion Nuclei by an Electrified Propane?Air Flame

The results are given of an investigation into the production and electrostatic precipitation of combustion nuclei by an electrified propane-air flame. The apparatus consisted of a burner with a dc potential applied which was supported inside a grounded metal combustion chamber where the generation and removal of particles could be studied. A mathematical and experimental analysis of transient combustion nuclei concentrations inside the combustion chamber was carried out to evaluate the nuclei precipitation and production rates as a function of flame potentials and air flow rates. Two new theoretical equations containing production, precipitation, and flow parameters are derived to describe these transient concentrations. The constants of the equations were determined by experiment. These lead directly to the important parameters of nuclei production and precipitation rates, which are difficult to assess individually using previously known techniques. The experiments show that the concentration of combustion nuclei in the exhaust gas can be significantly decreased by the simple electrification of the flame. For combustion processes that generate aerosols, the method has the advantage of using the flame itself to affect the removal of the particles from the exhaust gases. Since combustion nuclei are receiving increased attention as air pollutants, this study could have important practical applications.     

Monitoring and estimating concentrations of polychlorinated biphenyls, dioxins, and furans in cattle milk and soils of Rhine-Delta floodplains

Neuregulins have become the focus of intense research due to their putative roles in the etiology of certain cancers and to their evolving roles in PNS and CNS development. Evidence has been presented that neuregulins are present in neuronal cells where they act as mediators of neuron-glial signaling. Consistent with this view, we now report that there is a dramatic differential response of Schwann cells to the two major isoforms of neu differentiation factor (NDF alpha and NDF beta). NDF beta is a potent mitogen, whereas NDF alpha is nonmitogenic for Schwann cells. In addition, we report that Schwann cells contain endogenous NDF as well as the mRNA for both isoforms of NDF. Evidence is also presented that several isoforms of NDF are released from cultured Schwann cells. Our data suggest that in addition to functioning as a neuron-glial mediator, endogenous neuregulins may function in an autocrine/paracrine loop or in a juxtacrine- (cell-to-cell) mediated signal between individual Schwann cells or between Schwann cells and neurons.     

On the use of modal derivatives for nonlinear model order reduction

Modal derivative is an approach to compute a reduced basis for model order reduction of large‐scale nonlinear systems that typically stem from the discretization of partial differential equations. In this way, a complex nonlinear simulation model can be integrated into an optimization problem or the design of a controller, based on the resulting small‐scale state‐space model. We investigate the approximation properties of modal derivatives analytically and thus lay a theoretical foundation of their use in model order reduction, which has been missing so far. Concentrating on the application field of structural mechanics and structural dynamics, we show that the concept of modal derivatives can also be applied as nonlinear extension of the Craig–Bampton family of methods for substructuring. We furthermore generalize the approach from a pure projection scheme to a novel reduced‐order modeling method that replaces all nonlinear terms by quadratic expressions in the reduced state variables. This complexity reduction leads to a frequency‐preserving nonlinear quadratic state‐space model. Numerical examples with carefully chosen nonlinear model problems and three‐dimensional nonlinear elasticity confirm the analytical properties of the modal derivative reduction and show the potential of the proposed novel complexity reduction methods, along with the current limitations. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigating collection 4 versus collection 5 MODIS 250 m NDVI time-series data for crop separability in Kansas,USA

The primary objective of this research was to analyse collection 5 versus collection 4 time-series normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m for the purpose of separating crop types. Using extensive ground reference data from the state of Kansas in the central USA, NDVI value profiles were extracted from different collection versions for 2001 (collections 4 and 5) and 2005 (collection 5 only). Phenological curves for all crops and all data sets were created and visually inspected. Jeffries–Matusita (J-M) distance statistical analysis was performed to assess crop separability. Contrary to expectations, collection 5 time-series MODIS 250 m NDVI data were found to be inferior to collection 4 with respect to crop separability. Specifically, collection 4 data exhibited a greater dynamic range across the growing seasons of the various crop types, and this discriminatory advantage was supported by J-M distance analysis. Though the analysis did not suggest reasons for the outcome, it corroborates the conclusion of the only other similar study in the literature comparing data from collections 4 and 5. Considering the pervasive use of these data for land-cover mapping, it is recommended that MODIS NDVI data from collection 4 should be used where possible for crop type mapping in agricultural regions with climate, geography, and crops similar to Kansas.     

Vocational education approach: New TEL settings—new prospects for teachers’ instructional activities?

This study focuses on vocational education teachers’ instructional activities in a new technology-enhanced learning (TEL) setting. A content analysis is applied to investigate teachers’ and students’ interactions in a 3D game context. The findings illustrate that when teachers’ and students’ interactions are mediated by a game, teachers seem to apply different discussion activities to empower vocational learning than they do in traditional classroom settings. Additionally, the present study shows that teachers spontaneously develop new ways of supporting vocational learning processes. In more detail, two main types of instructional activities were identified: a “knowledge-providing” approach and a “joint problem-solving” approach. Additionally, findings illustrate how teachers using different types of instructional approaches are followed up with different processes by students. The article is concluded with a general discussion of the emerging challenges regarding the technological and pedagogical development of vocational education and teachers’ instructional activities in new TEL settings based on a more long-term design-based research project (ongoing since 2004).