Electro-optic response of an antiferroelectric liquid crystal in submicron cells

The dynamics of chiral smectic phases of antiferroelectric liquid crystal MHPOBC in a confined geometry has been analysed. Using an electro-optic response technique, the temperature dependences of the relaxation rates and electro-optic strengths of the elementary excitations in thin, planar aligned, wedge-type cells of thickness from 0.3 to 4 μm have been measured and compared with those for a 50 μm hometropically aligned cell. The effects of the confined geometry are the following. (i) The smectic C^* _γ phase does not exist in planar aligned cells with thickness less than 4 μm. Instead of this phase, we have observed the coexistence of the ferroelectric smectic C^* phase and the antiferroelectric smectic C^* _A phase over a very wide temperature range. (ii) The smectic C^* _α phase is stable at all measured thicknesses down to 0.3 μm. (iii) We have observed a decrease of the smectic A-smectic C^* _α phase transition temperature, proportional to the inverse of the cell thickness. (iv) Additional, thickness-independent phase modes have been observed above some critical value of the measuring electric field in all tilted phases.     

AFM study of forces in and structures of nematic liquid crystal interfaces on silanated glass

We have studied interfacial forces in MBBA, 5CB, 8CB and 12CB liquid crystals on DMOAP silanated glass substrates using a temperature controlled AFM in the force spectroscopy mode. In the bulk isotropic phase all these interfaces are clearly divided into two regions. The first molecular layer, which is absorbed to the glass surface, is smectic-like and shows submicron holes; this layer covers approximately 70% of the surface and is in all cases stable far beyond the clearing point. It is followed by a partially ordered region, which is different for different materials. We observe pre-nematic ordering in 5CB, pre-smectic ordering in 8CB and well developed layer-by-layer ordering in 12CB.     

Synthesis and Characterization of Diethyl Fumarate‐1,4‐Cyclohexanedimethanol Polyesters for Use in Bioresorbable Bone Cement Composites

Unsaturated polyesters are prepared by transesterification polymerization of diethyl fumarate and 1,4‐cyclohexanedimethanol. The structure of the polyesters was characterized by FT‐IR and ¹H‐ and ¹³C‐NMR spectroscopy. Semicrystalline morphology of the polymers is suggested by DSC analysis with T_g at 21°C and melting at 140°C. The thermogravimetric analysis indicated that the onset of degradation takes place at 300°C. The polyester's structure has significant impact on the properties of the composites prepared by crosslinking the fumarate double bonds with N‐vinyl pyrrolidone in the presence of an inorganic filler, calcium sulfate dihydrate, with the addition of a radical initiator, benzoyl peroxide, at ambient temperatures. The compressive strength and hydrolytic stability of the cement compositions was correlated with structure of the polyesters.     

Characterization of partially inverse spinel ZnFe2O4 with high saturation magnetization synthesized via soft mechanochemically assisted route

ZnFe₂O₄ was prepared by a soft mechanochemical route from two starting combinations of powders: (1) Zn(OH)₂/α-Fe₂O₃ and (2) Zn(OH)₂/Fe(OH)₃ mixed in a planetary ball mill. The mechanochemical treatment provoked reaction leading to the formation of the ZnFe₂O₄ spinel phase that was monitored by XRD, TEM, IR and Raman spectroscopy. The spinel phase was first observed after 4 h of milling and its formation was completed after 18 h in both the cases of starting precursors. The synthesized ZnFe₂O₄ has a nanocrystalline structure with a crystallite size of about 20.3 and 17.6 nm, for the cases (1) and (2), respectively. In the far-infrared reflectivity spectra are seen four active modes. Raman spectra suggest an existence of mixed spinel structure in the obtained nanosamples. In order to confirm phase formation and cation arrangement, Mössbauer measurements were done. Estimated degree of inversion is about 0.58 for both starting mixtures. The magnetic properties of the prepared ZnFe₂O₄ powders were also studied. The results show that the samples have a typical superparamagnetic-like behavior at room temperature. Higher values of magnetization in the case of samples obtained with starting mixture (2) suggest somewhat higher degree of cation inversion.     

Scattering and Localization Properties of Highly Oscillatory Potentials

We investigate scattering, localization, and dispersive time decay properties for the one‐dimensional Schrödinger equation with a rapidly oscillating and spatially localized potential , where is periodic and mean zero with respect to y. Such potentials model a microstructured medium. Homogenization theory fails to capture the correct low‐energy (k small) behavior of scattering quantities, e.g., the transmission coefficient as ? tends to zero. We derive an effective potential well such that is small, uniformly for as well as in any bounded subset of a suitable complex strip. Within such a bounded subset, the scaled limit of the transmission coefficient has a universal form, depending on a single parameter, which is computable from the effective potential. A consequence is that if ?, the scale of oscillation of the microstructure potential, is sufficiently small, then there is a pole of the transmission coefficient (and hence of the resolvent) in the upper half‐plane on the imaginary axis at a distance of order from . It follows that the Schrödinger operator has an bound state with negative energy situated a distance from the edge of the continuous spectrum. Finally, we use this detailed information to prove the local energy time decay estimate: where denotes the projection onto the continuous spectral part of . © 2013 Wiley Periodicals, Inc.     

Some Considerations in Relation to the Matrix Equation AXB = C

In this paper we represent a new form of condition for the consistency of the matrix equation AXB = C. If the matrix equation AXB = C is consistent, we determine a form of general solution which contains both reproductive and non-reproductive solutions. Also, we consider applications of the concept of reproductivity for obtaining general solutions of some matrix systems which are in relation to the matrix equation AXB = C.     

A comparison of alkaline and proton exchange membrane electrolyzers

Faraday efficiencies and energy consumptions of a small commercial proton exchange membrane (PEM) and an alkaline electrolyzer designed at our laboratory and equipped with different cathode materials were determined. Our experimental data indicate that the alkaline electrolyzer has a higher Faraday efficiency than the PEM electrolyzer, but, on the other hand, less energy is required for the PEM electrolyzer compared with the alkaline one. The results are discussed with regard to the special advantages of electrolyzers of both types. The text was submitted by the authors in English.     

On Jordan Triple Derivations and Related Mappings

In this article we study certain functional equations and systems of functional equations related to (generalized) derivations on semiprime rings. In particular, we prove that any generalized Jordan triple derivation on a 2- torsion free semiprime ring is a generalized derivation. We also prove that any (generalized) Jordan triple *-derivation on a 2-torsion free semiprime *-ring is a (generalized) Jordan *-derivation. The second author was supported in part by the Ministry of Science, Education and Sports of the Republic of Croatia (project No. 037-0372784-2757).     

Cellular uptake mechanisms and endosomal trafficking of supercharged proteins

Supercharged proteins (SCPs) can deliver functional macromolecules into the cytoplasm of mammalian cells more potently than unstructured cationic peptides. Thus far, neither the structural features of SCPs that determine their delivery effectiveness nor their intracellular fate postendocytosis, has been studied. Using a large set of supercharged GFP (scGFP) variants, we found that the level of cellular uptake is sigmoidally related to net charge and that scGFPs enter cells through multiple pathways, including clathrin-dependent endocytosis and macropinocytosis. SCPs activate Rho and ERK1/2 and also alter the endocytosis of transferrin and EGF. Finally, we discovered that the intracellular trafficking of endosomes containing scGFPs is altered in a manner that correlates with protein delivery potency. Collectively, our findings establish basic structure-activity relationships of SCPs and implicate the modulation of endosomal trafficking as a determinant of macromolecule delivery efficiency.