Magnetically activated micromixers for separation membranes

Presented here is a radically novel approach to reduce concentration polarization and, potentially, also fouling by colloids present in aqueous feeds: magnetically responsive micromixing membranes. Hydrophilic polymer chains, poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted via controlled surface-initiated atom transfer radical polymerization (SI-ATRP) on the surface of polyamide composite nanofiltration (NF) membranes and then end-capped with superparamagnetic iron oxide magnetite (Fe(3)O(4)) nanoparticles. The results of all functionalization steps, that is, bromide ATRP initiator immobilization, SI-ATRP, conversion of PHEMA end groups from bromide to amine, and carboxyl-functional Fe(3)O(4) nanoparticle immobilization via peptide coupling, have been confirmed by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). These nanoparticles experience a magnetic force as well as a torque under an oscillating external magnetic field. It has been shown, using particle image velocimetry (PIV), that the resulting movement of the polymer brushes at certain magnetic field frequencies induces mixing directly above the membrane surface. Furthermore, it was demonstrated that with such membranes the NF performance could significantly be improved (increase of flux and salt rejection) by an oscillating magnetic field, which can be explained by a reduced concentration polarization in the boundary layer. However, the proof-of-concept presented here for the active alteration of macroscopic flow via surface-anchored micromixers based on polymer-nanoparticle conjugates has much broader implications.     

On the restriction of cross characteristic representations of 2 F 4(q) to proper subgroups

We prove that the restriction of any nontrivial representation of the Ree groups ² F ₄(q), q = 2²ⁿ⁺¹ ≥ 8 in odd characteristic to any proper subgroup is reducible. We also determine all triples (K, V, H) such that ${K \in \{^2F_4(2), ^2F_4(2)'\} }We prove that the restriction of any nontrivial representation of the Ree groups ² F ₄(q), q = 2²ⁿ⁺¹ ≥ 8 in odd characteristic to any proper subgroup is reducible. We also determine all triples (K, V, H) such that K ? {²F₄(2), ²F₄(2)￠}{K \in \{^2F_4(2), ^2F_4(2)'\} } , H is a proper subgroup of K, and V is a representation of K in odd characteristic restricting absolutely irreducibly to H.     

Characterization of PDMS model junctions and networks by solution and solid-state silicon-29 NMR spectroscopy

The application of ²⁹Si solution and solid-state cross-polarization/magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) techniques to the study of structural features in polydimethylsiloxane (PDMS) model endlinked elastomeric networks is explored. The relationship between the topological (network) functionality of a structural moiety, which determines network mechanical properties, and its chemical (spectral) functionality, which is reported by the NMR, is discussed. The second-order spectral shifts corresponding to topographical functionality variation within a chemical functionality class are usually sufficiently well resolved in these networks to allow positive identification of a variety of structural features. The basic PDMS repeat unit, ? OSi(CH₃)₂? , is found to possess an axially symmetric chemical shift tensor with σ_∥ = ?56.8 ppm downfield from TMS, and σ_⊥ = ?4.4 ppm. This axial symmetry does not result from rapid reorientation about the chain axis. The NMR spectrum reveals defects in model endlinked networks. In the case of vinyl-endlinked systems, the defects are ascribed to the formation of elastically ineffective loops. Hydroxyl-endlinked systems contain either loops or else trifunctional junctions (hydrolyzed before chain coupling could take place) and dangling chain ends. The CP/MAS technique provides an order-of-magnitude reduction over standard solution techniques in the time to acquire a spectrum from a network not containing paramagnetic doping. ¹³C spectra of PDMS systems are not as informative as ²⁹Si spectra.     

HPTLC-Bestimmung von Paracetamol im Serum

Ohne Zusammenfassung

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Determination of paracetamol in serum by HPTLC

     

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2x Al x Cr x O4

In order to study the effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al _x Cr _x Fe_2.5?2x O₄ (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5).     

联苯胺分光光度法测定食盐中碘含量

基于在盐酸介质中,碘酸钾氧化联苯胺使其显色,提出了光度法测定食盐中微量碘的方法。在40℃的水浴中,当2 mol.L-1盐酸溶液用量为1.00 mL0、.42 g.L-1联苯胺溶液用量为0.80 mL时,方法的线性范围为100~1 400μg.L-1,最大吸收波长在425 nm处,表观摩尔吸光率为1.4×105L.mol-1.cm-1。用于测定加碘食盐中碘含量的测定,回收率在97.5%~101.2%之间,相对标准偏差(n=7)在0.9%~1.9%之间。     

Literatur

Ohne Zusammenfassung     

Dade's Invariant Conjecture for the Symplectic Group Sp4(2 n ) and the Special Unitary Group SU4(22n ) in Defining Characteristic

In this article, we verify Dade's projective invariant conjecture for the symplectic group Sp₄(2 ⁿ ) and the special unitary group SU₄(2²ⁿ ) in the defining characteristic, that is, in characteristic 2. Furthermore, we show that the Isaacs–Malle–Navarro version of the McKay conjecture holds for Sp₄(2 ⁿ ) and SU₄(2²ⁿ ) in the defining characteristic, that is, Sp₄(2 ⁿ ) and SU₄(2²ⁿ ) are good for the prime 2 in the sense of Isaacs, Malle, and Navarro.