Ferromagnetism in magnetically doped III-V semiconductors

The origin of ferromagnetism in semimagnetic III-V materials is discussed. The indirect exchange interaction caused by virtual electron excitations from magnetic impurity level in the bandgap to the valence band can explain ferromagnetism in GaAs(Mn) no matter samples are degenerated or not. Formation of ferromagnetic clusters and percolation picture of phase transition describes well all available experimental data and allows to predict the Mn-composition dependence of transition temperature in wurtzite (Ga,In,Al)N epitaxial layers.Comment: 4 pages with 3 figure

1,10-diaza-18-crown-ether, modified by phosphonate pendant arms - Synthesis, structure, and picrate extraction properties

Reaction of O,O′-diisopropyl-3-methyl-1,2-butadienylphosphonate with 1,10-diaza-18-crown-6 in the presence of a catalytic amount of iPrONa leads to the new crown-ether derivative, containing phosphonate pendant arms (L). The structure of the compound obtained was investigated by single crystal X-ray diffraction analysis, IR, 1H and 31P{1H} NMR spectroscopy, and microanalysis. In the crystal structure the side arms of L are in an anti disposition relative to the macrocyclic cavity. It was established that phosphorylation of 1,10-diaza-18-crown-6 by allenylphosphonate results in an increase of extraction of NaPic and KPic, whereas LiPic and NH4Pic are extracted practically in the same level. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA

Compression-induced structural and mechanical changes of fibrin-collagen composites

Fibrin and collagen as well as their combinations play an important biological role in tissue regeneration and are widely employed in surgery as fleeces or sealants and in bioengineering as tissue scaffolds. Earlier studies demonstrated that fibrin-collagen composite networks displayed improved tensile mechanical properties compared to the isolated protein matrices. Unlike previous studies, here unconfined compression was applied to a fibrin-collagen filamentous polymer composite matrix to study its structural and mechanical responses to compressive deformation. Combining collagen with fibrin resulted in formation of a composite hydrogel exhibiting synergistic mechanical properties compared to the isolated fibrin and collagen matrices. Specifically, the composite matrix revealed a one order of magnitude increase in the shear storage modulus at compressive strains>0.8 in response to compression compared to the mechanical features of individual components. These material enhancements were attributed to the observed structural alterations, such as network density changes, an increase in connectivity along with criss-crossing, and bundling of fibers. In addition, the compressed composite collagen/fibrin networks revealed a non-linear transformation of their viscoelastic properties with softening and stiffening regimes. These transitions were shown to depend on protein concentrations. Namely, a decrease in protein content drastically affected the mechanical response of the networks to compression by shifting the onset of stiffening to higher degrees of compression. Since both natural and artificially composed extracellular matrices experience compression in various (patho)physiological conditions, our results provide new insights into the structural biomechanics of the polymeric composite matrix that can help to create fibrin-collagen sealants, sponges, and tissue scaffolds with tunable and predictable mechanical properties

Regioselective alkylation of the lower rim of p-tert-butylthiacalix[4]arene with n-(p-nitrophenyl)-α-bromoacetamide

The preparation of partially substituted thiacalix[4]arenes 2-6 has been accomplished by conducting the reaction of the thiacalixarene 1 with N-(p-nitrophenyl)-α-bromoacetamide in acetone or acetonitrile in the presence of M2CO3 (M = Na, K and Cs). The influence of the reaction conditions (temperature, time, solvent, ratio of the reagents and the nature of the alkali metal carbonate) on regio- and stereoselectivity of this reaction is described. © 2009 Taylor & Francis

Phosphorylation of p-tert-butylthiocalix[4]arene: Reaction with phosphorus trichloride

The synthesis of the first phosphorylated derivatives of p-tert-butylthiocalix[4]arene was achieved by reaction with phosphorus trichloride. The product containing two cyclic P(III) atoms is not hydrolytically stable. The flattened 1,2-alternate conformation of a P(IV) derivative was established by 1H, 13C, 31P NMR experiments and X-ray analysis

KP line solitons and Tamari lattices

The KP-II equation possesses a class of line soliton solutions which can be qualitatively described via a tropical approximation as a chain of rooted binary trees, except at "critical" events where a transition to a different rooted binary tree takes place. We prove that these correspond to maximal chains in Tamari lattices (which are poset structures on associahedra). We further derive results that allow to compute details of the evolution, including the critical events. Moreover, we present some insights into the structure of the more general line soliton solutions. All this yields a characterization of possible evolutions of line soliton patterns on a shallow fluid surface (provided that the KP-II approximation applies).Comment: 49 pages, 36 figures, second version: section 4 expande