Nonreductive deiodination of ortho-iodo-hydroxylated arenes using tertiary amines

A convenient and nonreductive deiodination is reported for the ortho-iodo-hydroxylated arenes including derivatives of quinolinol, phenol, and naphthol. Tertiary amines pyridine, triethylamine, and N-methylmorpholine in the presence of water initiated deiodination of ortho-iodo-hydroxylated arenes without affecting para-iodine and other reduction-susceptible groups. This reported method also works efficiently for polyiodinated systems. Simplicity, short reaction times, and absence of reducing catalyst are features of this method.     

Experimental estimation of the interaction parameter eO for ZnN

The use of dislocation measurements in Zinc single crystals reveals the presence of a yield point or flow stress corresponding to a Stages I–II (elastic to elastic-plastic) transition. This is commonly attributed to the presence of interstitials such as N. The mathematical models of Seeger and Dorn and Rajnak are used to evaluate certain microstructural parameters. These correlate favourably with experimental values. The excess work done over that to overcome the Peierls and frictional forces is then calculated per pair of pinning interstitials and equated to the energy of formation of a molecule of Zn₃N₂ which is believed to form. The results show that this assumption does lead to the stochiometry Zn₃N₂, thus verifying mathematical parameters from different equations using work-energy concepts. Use of the mechanical equivalent J also seems to indicate a favourable correlation for the stochiometry of Zn₃N₂, and for e_O as calculated calorimetrically.     

Imaging electron trajectories in a laser-wakefield cavity using betatron X-ray radiation

We demonstrate that betatron x-ray radiation accurately provides direct imaging of electrons trajectories accelerated in laser wakefields. Experimental far field x-ray beam profiles reveal that electrons can follow similar transverse trajectories with typical excursions of 1.5 microm+/-0.5 microm in the plane of laser polarization and 0.7 microm+/-0.2 microm in the plane perpendicular.     

Analysis and parametric optimization of 1H off-resonance relaxation NMR experiments designed to map polypeptide self-recognition and other noncovalent interactions

The measurement of 1H off-resonance nonselective relaxation rates (R(theta,ns)) has been recently proposed as an effective method to probe peptide self-recognition, opening new perspectives in the understanding of the prefibrillization oligomerization processes in amylodogenesis. However, a full analysis and parametric optimization of the NMR experiments designed to measure R(theta,ns) relaxation rates is still missing. Here we analyze the dependence of the R(theta,ns) rates upon three critical parameters: the tilt angle of the effective field during the spin lock, the static magnetic field, and finally the repetition delay. Our analysis reveals that the tilt angle theta = 35.5 degrees not only minimizes spin-diffusion, but also avoids experimental artifacts such as J-transfer and poor adiabaticity. In addition, we found that when the dominant relaxation mechanism is caused by uncorrelated pairwise 1H dipole-1H dipole interactions the R(35.5 degrees,ns) rate is not significantly affected by static field variations, suggesting a wide applicability of the 1H off-resonance nonselective relaxation experiment. Finally, we show that the self-recognition maps based on the comparative analysis of the R(35.5 degrees,ns) rates can tolerate decreases in the interscan delays without significantly compromising the identification of critical self-association loci. These considerations not only provide a better understanding of the 1H off-resonance nonselective relaxation, but they also serve as guidelines for the optimal setup of this experiment.     

Determination of carbon nanotube density by gradient sedimentation

Density gradient centrifugation is a high-resolution technique for the separation and characterization of large molecules and stable complexes. We have analyzed various nanotube structures by preparative centrifugation in sodium metatungstate-water solutions. Bundled, isolated and acid-treated single-walled nanotubes (SWNTs) and multiwall nanotubes (MWNTs) formed sharp bands at well-defined densities. The structure of the material in each band was confirmed by transmission electron microscopy and Raman spectroscopy. Our data suggest respective densities of 1.87, 2.13, 1.74, and 2.1 g/cm(3) for bundled, isolated, and acid-treated SWNTs and MWNTs. These measured results compare well with their calculated densities.     

Ytterbium-doped Y2O3 nanoparticle silica optical fibers for high power fiber lasers with suppressed photodarkening

We report efficient laser demonstration and spectroscopic characteristics of a Yb-doped Y₂O₃ (or Y₃Al₅O₁₂) nanoparticle silica fiber developed by conventional fiber fabrication technique. The spectroscopy study evidences modification in the environment of Yb ions by the Y₂O₃ nanoparticles. As a result, photodarkening induced loss is reduced by 20 times relative to Yb-doped aluminosilicate fibers. The fiber is suitable for power scaling with good laser slope efficiency of 79%.     

Topological Majorana and Dirac zero modes in superconducting vortex cores

We provide an argument based on flux insertion to show that certain superconductors with a nontrivial topological invariant have protected zero modes in their vortex cores. This argument has the flavor of a two-dimensional index theorem and applies to disordered systems as well. It also provides a new way of understanding the zero modes in the vortex cores of a spinless px+ipy superconductor. Applying this approach to superconductors with and without time-reversal and spin-rotational symmetry, we predict the necessary and sufficient conditions for protected zero modes to exist in their vortices.     

Multimodal nonlinear optical polarizing microscopy of long-range molecular order in liquid crystals

We demonstrate orientation-sensitive multimodal nonlinear optical polarizing microscopy capable of probing orientational, polar, and biaxial features of mesomorphic ordering in soft matter. This technique achieves simultaneous imaging in broadband coherent anti-Stokes Raman scattering, multiphoton excitation fluorescence, and multiharmonic generation polarizing microscopy modes and is based on the use of a single femtosecond laser and a photonic crystal fiber as sources of the probing light. We show the viability of this technique for mapping of three-dimensional patterns of molecular orientations and show that images obtained in different microscopy modes are consistent with each other.