Magnetic Resonance Microscopy of Heterogeneity in Polymer Electrolyte Membranes

Magnetic resonance microscopy of Nafion 117 is used to measure the spatial variation of solvent dynamics in protonated (acid form) membranes immersed in solvent. Spatial resolution allows determination of membrane material property heterogeneity via T ₂ and diffusion variations to be easily studied in the presence of strong free solvent signal. Variation of T ₂ and diffusion as a function of solvent methanol–water mole fraction is measured. Spatially averaged T ₂ and diffusion data are in general agreement with previous bulk nuclear magnetic resonance studies; however, significant disparities from sample to sample at fixed solvent concentration are present in the spatially averaged data. The variation is determined to be due to changes in solvent mobility within the membrane over scales of the order of 10 mm, indicating macroscale heterogeneity of the solvent saturated membrane morphology. Authors' address: Sarah L. Codd, Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59717-3800, USA     

Dispersion properties of electromagnetically induced transparency under the Doppler broadening

The influence of heat motion of atoms in gaseous media on the features of manifestation of electromagnetically induced transparency is investigated. Taking into account elastic and inelastic collisions, fairly general and compact analytical relations are derived for the absorption and refraction coefficients of the probe wave in the presence of high-power inducing radiation, resonant to the adjacent atomic transition. It is shown, that occurrence of narrow resonance structures in the Doppler absorption and refraction profile is due to “overlap” of effective resonance velocities of atoms. The atomic level splitting in the strong wave field is uniformly analyzed in the entire intensity range. Interference transparency in a particular region of the Doppler profile is found to be accompanied by high resonance dispersion of the refraction coefficient, which is important for generating slow radiation and controlling its parameters. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 56–62, March, 2007.     

Fluorescence studies of the intra-cellular distribution of zinc bis(thiosemicarbazone) complexes in human cancer cells

The uptake of zinc bis(thiosemicarbazone) complexes in human cancer cells has been studied by fluorescence microscopy and the cellular distribution established, including the degree of uptake in the nucleus.     

Magnetic structures in the Ca2Fe2−xAlxO5 system-II

Recent structure analyses of crystals with different compositions in the Ca₂Fe_2?xAl_xO₅ system have led to a reinterpretation of the magnetic ‘phase diagram’ of this system. In the composition range 0 ? x ? 1, there are at least three and possibly four different magnetic structures. At room temperature, and between x = 0·00 and x less than but near 0·60 (the exact boundary is not known), the magnetic structure belongs to magnetic space group Pcm′n′; in a narrower range, approximately 0·57 ? x ? 0·65, the magnetic space group is I_pb′m′2; for x greater than about 0·80, the magnetic space group is I_pbm′2′. There is a substantial region of x and T (at room temperature 0·65 ? x ? 0·80), for which our experimental results cannot distinguish between two possibilities: either both the I_pb′m′2 and I_pbm′2′ structures coexist with spin-flipping as x or T changes or there is a continuous rotation of the spins with changing x or T. In the latter case, the most probable single magnetic space group in this region is C_pm′; with increasing x or T the transitions occur by way of I_pb′m′2 → C_pm′ → I_pbm′2′.     

Specific coil noise induced by magnetic matter at phase transition temperature

It was found that a polycrystalline gadolinium sample forming part of a closed magnetic loop threading a coil induced substantial coil noise when its temperature corresponded to the transition temperature of gadolinium.     

A complete analysis of a model nonlinear singular perturbation problem having a continuous locus of singular points

Consider the boundary value problem ?y′′ = (y² ? t²)y′, ? 1 ≤ t ≤ 0, y(? 1) = A, y(0) = B. Depending on the choice of A and B, one can ensure the existence of “turning points,” $\text{t}\text{?}\text{; y(t, ?)}{}^2\text{?}\text{t}\text{?}{}^2\text{= 0}$. However, due to the nonlinear nature of the problem, one does not know the position or number of such turning points. In the case when A >f 0 = B Kedem, Parter and Steuerwalt gave a development of this problem based on an abstract bifurcation analysis which in turn was based on “degree theory.” In this paper we give a complete analysis of the problem based entirely on a priori estimates and the “shooting” method.     

Recognizing graphic matroids

There is no polynomially bounded algorithm to test if a matroid (presented by an “independence oracle”) is binary. However, there is one to test graphicness. Finding this extends work of previous authors, who have given algorithms to test binary matroids for graphicness. Our main tool is a new result that ifM′ is the polygon matroid of a graphG, andM is a different matroid onE(G) with the same rank, then there is a vertex ofG whose star is not a cocircuit ofM.     

On minors of non-binary matroids

No binary matroid has a minor isomorphic toU ₄ ² , the “four-point line”, and Tutte showed that, conversely, every non-binary matroid has aU ₄ ² minor. However, more can be said about the element sets ofU ₄ ² minors and their distribution. Bixby characterized those elements which are inU ₄ ² minors; a matroidM has aU ₄ ² minor using elementx if and only if the connected component ofM containingx is non-binary. We give a similar (but more complicated) characterization for pairs of elements. In particular, we prove that for every two elements of a 3-connected non-binary matroid, there is aU ₄ ² minor using them both.     

Darstellung von Slockcopolymeren von Vinylacetat in viskosen schlechten L?sungsmitteln

Ohne Zusammenfassung