Illustration of a bimodal system in Intralipid-20% by polarized light scattering: experiments and modeling

Intralipid suspensions behave like phantoms of human tissues concerning their light scattering properties. We present experimental measurements of the angular distribution of polarized light scattering at various incidence angles on Intralipid-20%. A comparison of the absolute values of these measurements with simulations using a vector radiative transfer model (N-flux) developed for multilayered media demonstrates a stratified structure of the samples with a double distribution of the size of scatterers. This result is confirmed by polarimetry imaging.     

Optimizing ICA in fMRI using information on spatial regularities of the sources

Spatial independent component analysis (ICA) is a well-established technique for multivariate analysis of functional magnetic resonance imaging (fMRI) data. It blindly extracts spatiotemporal patterns of neural activity from functional measurements by seeking for sources that are maximally independent. Additional information on one or more sources (e.g., spatial regularity) is often available; however, it is not considered while looking for independent components. In the present work, we propose a new ICA algorithm based on the optimization of an objective function that accounts for both independence and other information on the sources or on the mixing model in a very general fashion. In particular, we apply this approach to fMRI data analysis and illustrate, by means of simulations, how inclusion of a spatial regularity term helps to recover the sources more effectively than with conventional ICA. The improvement is especially evident in high noise situations. Furthermore we employ the same approach on data sets from a complex mental imagery experiment, showing that consistency and physiological plausibility of relatively weak components are improved.     

FexNi100−x nanometric films deposited by laser ablation on SiO2/Si substrates

Fe_xNi_100−x nanometric films were deposited on SiO₂/Si substrates at room temperature using the pulsed laser deposition technique. The targets were Fe-Ni amorphous magnetic foils with composition Fe₅₀Ni₅₀, Fe₃₅Ni₆₅ and Fe₂₂Ni₇₈. Morphological and structural properties of the deposited films were investigated using scanning electron microscopy, Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, and X-ray reflectivity. Electrical and magnetic characteristics of the films were investigated by using the four-point probe and the magneto-optic Kerr effect techniques, respectively. The film properties are strictly dependent on the Fe-Ni compositional ratio.     

Absolute configuration of 1,n-diols by NMR: the importance of the combined anisotropic effects in bis-arylmethoxyacetates

The absolute configuration of a 1,n-diol can be assigned from the (1)H NMR spectra of its (R)- and (S)-AMAA diesters if the chemical shifts are interpreted as the result of the joint action of the two chiral auxiliaries.     

Method for intracellular magnetic labeling of human mononuclear cells using approved iron contrast agents

A method for intracellular iron labeling of human mononuclear cells (lymphocytes and monocytes) for magnetic resonance imaging (MRI) using simple incubation of cells with approved MRI iron contrast agents is presented. Labeled cells can be detected by MRI in vitro, and this suggests the possibility that the technique could become a marker for in vivo lymphocyte and monocyte trafficking studies in acute inflammatory lesions such as those in Multiple Sclerosis.     

Homogeneous Ziegler–Natta catalysis. II. Ethylene polymerization by IVB transition metal complexes/methyl aluminoxane catalyst systems

Homogeneous Ziegler-Natta systems for the ethylene polymerization, deriving from R₂R_2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ-alkyl and the π-cyclo-pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ-alkyl derivatives of IVB transition metals, such as Zr(CH₂C₆H₅)₄, are also able to polymerize ethylene with a fairly high productivity. Active species containing Zr? O? Al bonds have been postulated.     

Oxygenation of calixarene phenol rings

[structure: see text] The first examples of epoxy-p-quinol and diepoxy-p-quinol calixarene derivatives have been obtained by base-promoted direct addition of O(2)(oxygenation) to calixarene phenol rings. The regio- and stereochemistry of these derivatives was determined by 2D NMR studies, in conjunction with MM3 calculations, and X-ray crystallography. Both the oxygenation and the subsequent carbonyl reduction occur with a preferential attack to the less hindered exo face of the calixarene rings.     

Optimized Mueller polarimeter with liquid crystals

We demonstrate a Mueller polarimeter in which the polarization-state generator and analyzer are both composed of a linear polarizer and two liquid-crystal variable retarders. The polarimeter is designed to optimize the accuracy of the final results by minimization of the condition numbers of the modulation and analysis matrices. The polarimeter calibration, a difficult task by conventional procedures, is achieved easily by use of the eigenvalue method of Compain et al. [Appl. Opt. 38, 3490 (1999)]. The overall polarimeter performance is tested with a linear polarizer at various angles and a compensator at various retardations.