Rheological aspects of dense lignite–water suspensions; structure development on consecutive flow loops

Aspects of dense lignite–water slurries (LWS) rheology were investigated using controlled stress and controlled strain rheometers with parallel disks and Couette geometries. During the preparation of the slurries, the achieved solids volume fractions were up to 0.425 and the particle size distributions were polydispersed with sizes up to 300 μm. In the ascending parts of consecutive flow loops, a slope transition of the flow curve was observed and studied in relation to the solids volume fraction. The obtained results with the different geometries and rheometers were qualitatively the same. By following the model proposed by Cheng (Rheol Acta 42:372–382, 2003) for thixotropic fluids, and taking into account the yield stress appearance, a suitable correlation for LWS is proposed, which is consistent with the experimental flow curves.     

Rheological aspects of dense lignite-water suspensions; time dependence, preshear and solids loading effects

An investigation of the rheological properties of dense lignite-water suspensions is reported here in order to evaluate the parameters that affect the rheology of these suspensions. Different types of particle size distributions were achieved via wet grinding with particle sizes down to 1 μm. Polyelectrolytes and surfactants were used to improve the stability and rheology of suspensions. The achieved solid volume fraction, φ, with acceptable rheological behavior was 0.45, while the ratio of φ/φ _m was close to 0.85; φ _m is the maximum solid volume fraction. Various types of flow tests were performed on lignite-water suspensions with various preshear times and stress levels. Typical shear rates varied in the range between 10^–2 to 10² s^–1. The low shear behavior was found to be quite different from the high shear behavior for the most concentrated suspensions, with a plateau value at low shear rates indicating the appearance of a yield stress. These plateau values, however, depend on shear history, which is responsible for the development of different structures in the sample. The viscosity curves corresponding to the ascending and descending parts of the flow curve were found to be different; these flow curve parts can be described either by well established models or by modified ones. The non-Newtonian time dependent behavior of the lignite-water suspensions is attributed to the high value of the ratio φ/φ _m , the polydispersity of the particle size distribution, and the non-spherical shape of the lignite particles.     

Łoś's theorem and the axiom of choice

In set theory without the Axiom of Choice ( $\mathsf{AC}$), we investigate the problem of the placement of ?o?'s Theorem ( $\mathsf{LT}$) in the hierarchy of weak choice principles, and answer several open questions from the book Consequences of the Axiom of Choice by Howard and Rubin, as well as an open question by Brunner. We prove a number of results summarised in § 3.     

Neutron activation analysis for determination of metal ions in biological fluids of patients after CoCrMo arthroplasty

Determination of metals and trace elements in patients with total knee or hip arthroplasty with CoCrMo alloy was performed. Blood, urine and cerebrospinal fluid (CSF) samples were analyzed and compared with samples from healthy people. Levels of Co, Cr as well as Na, Ca, Fe, Zn, Se, Rb, Sb and Br were determined by means of neutron activation analysis. The values of Cr and Co of the blood and urine measurements were elevated in patients with replacement, and according to the statistical analysis, significant differences of the elements Zn, Br, Co and Sb were found in the CSF (p?<?0.05).

     

An experimental and theoretical study of butyl methacrylate in situ radical polymerization kinetics in the presence of graphene oxide nanoadditive

The butyl methacrylate radical polymerization kinetics in the presence of graphene oxide nanoadditive is studied both experimentally and theoretically. The experimental study includes the formation of graphite oxide from the oxidation of graphite and its subsequent transformation to graphene oxide (GO) after ultrasonication and in situ polymerization. Monomer conversion versus time was monitored gravimetrically at various reaction temperatures and initial GO fractions. Formation of GO was verified by X‐ray diffraction spectra and the number and weight average molecular weights of the final polymer were obtained from GPC measurements. A detailed theoretical kinetic model was further developed. The model predictions were found to be in satisfactory agreement with the experimental data. The presence of GO was found to result in reduced initiator efficiency verified theoretically and explained through side reactions of primary radicals. Finally, nanocomposites showed enhanced thermal stability compared to neat PBMA. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1433–1441     

Winterberg’s Conjectured Breaking of the Superluminal Quantum Correlations over Large Distances

We elaborate further on a hypothesis by Winterberg that turbulent fluctuations of the zero point field may lead to a breakdown of the superluminal quantum correlations over very large distances. A phenomenological model that was proposed by Winterberg to estimate the transition scale of the conjectured breakdown, does not lead to a distance that is large enough to be agreeable with recent experiments. We consider, but rule out, the possibility of a steeper slope in the energy spectrum of the turbulent fluctuations, due to compressibility, as a possible mechanism that may lead to an increased lower-bound for the transition scale. Instead, we argue that Winterberg overestimated the intensity of the ZPF turbulent fluctuations. We calculate a very generous corrected lower bound for the transition distance which is consistent with current experiments.     

Examples Illustrating the Use of Renormalization Techniques for Singularly Perturbed Differential Equations

With nine examples, we seek to illustrate the utility of the Renormalization Group approach as a unification of other asymptotic and perturbation methods.     

Sharp integral inequalities for the dyadic maximal operator and applications

Mathematische Zeitschrift - We prove a sharp integral inequality for the dyadic maximal function of $$\phi \in L^p$$ . This inequality connects certain quantities related to integrals of $$\phi $$...     

Chemical characterization of particulate matter (PM) and source apportionment study during winter and summer period for the city of Kozani,Greece

Eordaia basin located in northwest of Greece, comprises an area which is characterized by intense energy related activities, including coal burning at four power plants and the associated mining operations. Air samples of inhalable (PM10) and respirable particles (PM2.5) were collected in cold and warm periods in 2010 at an urban background site of Kozani, the major city and capital of the region which is located close to the power plants. Particulate matter concentration, particle-bound polycyclic aromatic hydrocarbons and anionic species concentrations were determined using gravimetric, GC-MS in SIM mode and Ion Chromatography analysis, respectively. For the cold period, the mean PM10 and PM2.5 mass concentration was found to be 19.62 and 14.68 µg m^?3, respectively. Correspondingly, for the warm period, the mean PM10 and PM2.5 values were 35.29 and 25.75 µg m^?3, respectively. In general, the results indicated that the major sources of air pollution in Kozani are traffic, combustion from agricultural activities and lignite power plants emissions, contributing by different percentages to each particle fraction.