Field strengths of 164 kHz radio-waves received at Ahmedabad from Tashkent in 1960–65 and effect of solar X-ray emissions

The paper summarises the results of observations on the field strength of 164 kHz radio-waves received at Ahmedabad from Tashkent during the period 1960–65. There is a general increase in field strength with decrease in solar activity. From the end of 1965 when we began to receive X-ray data from N.R.L. satellites, it has been noticed that increases in the intensity of 0–8 Å at satellite level, are associated with daytime decreases in the field strength of 164 kHz waves received at Ahmedabad. As may be expected, the enhancement of 0–8 Å X-rays is also associated in a general way with an increased emission from the sun of 10·7 cm. radio-waves. Examples are given.     

Viscoelasticity of dynamically self-assembled paramagnetic colloidal clusters

Paramagnetic particles in a liquid above a solid dynamically self-assemble into two-dimensional (2D) viscoelastic clusters in a processing magnetic field if the precession angle exceeds the magic angle. Hexagonal clusters rotate with a frequency proportional to the precession frequency of the magnetic field. The rotation is explained by viscoelastic shear waves excited in the clusters that can be visualized slightly above the magic angle. The cluster rotation and the visualization of viscoelastic modes are independent techniques to probe the rheological properties of the cluster. We find agreement between both techniques when determining the 2D cluster viscosity eta(c) approximately 10(-11) N s/m.     

Enhanced hydrogen generation by particles during sonochemical decomposition of water

A novel effect of any oxide particle/intermetallics enhancing hydrogen generation from water as compared to water alone when subjected to ultrasonic irradiation is reported here. Addition of methanol to water or decrease in particle size also improved the hydrogen yield. Hydrogen generation from water was further enhanced by the presence of both methanol and particles in water.     

Analyses of the complex proton NMR spectra: determination of anisotropic proton chemical shifts of oriented molecules by a two dimensional experiment

NMR spectra of molecules oriented in the liquid crystalline media provide information on the molecular structure and order parameter. However, the numerical iterative analysis of the proton spectra of strongly coupled spins is difficult and time consuming. Such analysis is simplified if nearly accurate starting parameters are available. One such parameter is the chemical shift which in the oriented media is very different from the isotropic values due to anisotropic contributions. In this study, we have explored the possibility of obtaining chemical shifts in the oriented phase to aid the analysis of the spectra. A two dimensional experiment in which FSLG decoupling employed during the t1 period eliminates the homonuclear dipolar couplings and retains only the chemical shifts has been implemented. Experiments on the molecule cis,cis-mucononitrile demonstrate that the chemical shifts obtained by this procedure are nearly the same as the chemical shifts derived by iterative analysis of the one dimensional spectrum of the molecule following the standard procedure. The method has also been used to analyse the spectrum of 1-iodopropane using the chemical shifts obtained from the proposed experiment as the starting parameters.     

Simulations of information transport in spin chains

Transport of quantum information in linear spin chains has been the subject of much theoretical work. Experimental studies by NMR in solid state spin systems (a natural implementation of such models) is complicated since the dipolar Hamiltonian is not solely comprised of nearest-neighbor XY-Heisenberg couplings. We present here a similarity transformation between the XY Hamiltonian and the double-quantum Hamiltonian, an interaction which is achievable with the collective control provided by radio-frequency pulses. Not only can this second Hamiltonian simulate the information transport in a spin chain, but it also creates coherent states, whose intensities give an experimental signature of the transport. This scheme makes it possible to study experimentally the transport of polarization beyond exactly solvable models and explore the appearance of quantum coherence and interference effects.     

Synthesis, mechanism of formation, and dynamics of a highly fluorinated methylenecyclobutene

Treatment of the hydrazone of 2H-perfluoro-2-methyl-3-pentanone with triethylamine at elevated temperatures yields a methylenecyclobutene via degradation to an acetylene followed by dimerization. The dimerization occurs even at -78 degrees C, and details of the reaction pathway have been elucidated. Both the acidity and the conformational dynamics of the methylenecyclobutene are influenced by buttressing effects in this crowded molecule.     

Probing the intramolecular hydrogen bond of 2-(2-hydroxyphenyl)benzotriazoles in polar environment: a photophysical study of UV absorber efficiency

An in-depth photophysical study is presented for a series of 2-(2-hydroxyphenyl)benzotriazoles (HBzTs); the structural characteristic of all these photostabilizers is their strong intramolecular hydrogen bridge (IMHB). Tinuvin P (TIN P, 11a) and six other HBzTs, with no substituent in the 3'-position ortho to the hydroxy function, show pronounced phosphorescence already in the dark (at 77 K in a polar glass). Upon irradiation, the phosphorescence intensity rises further until an equilibrium value is attained (up to 1.5 fold the dark value). A kinetic model is given which excellently reproduces this phosphorescence evolution: it demonstrates phosphorescence to arise from open conformers where the IMHB has been broken. Phosphorescence excitation spectra match the absorption spectra of the open conformer and also that of the O-methyl homologue 11A which cannot form an IMHB. Fluorescence spectra likewise prove the equilibrium between the closed and open conformer for these HBzTs. In unpolar glasses as well as in the crystalline state, TIN P displays a long-wavelength (red) fluorescence (with an enormous Stokes shift of approximately 10.000 cm-1) which is associated with the excited singlet state of the closed form after proton transfer within the IMHB, S1'(C). In polar matrixes, on the other hand, a blue fluorescence is observed (with a regular Stokes shift) for all those HBzTs which have no 3'-substituent shielding the IMHB against being opened by the polar solvent. This blue fluorescence, just as the characteristic phosphorescence evolution for these compounds, is associated with the open conformer. For HBzTs with an (alkyl) group ortho to the bridging OH group, however, a long-wavelength (red) fluorescence is again observed. The shielding effect of the 3'-substituent shows a fine gradation, cumyl >/= 1,1,3,3-tetramethylbutyl (isooctyl) > t-butyl >/= methyl.     

Pullulan hydrogels improve mesenchymal stem cell delivery into high-oxidative-stress wounds

Cell-based therapies for wound repair are limited by inefficient delivery systems that fail to protect cells from the acute inflammatory environment. Here, a biomimetic hydrogel system is described that is based on the polymer pullulan, a carbohydrate glucan known to exhibit potent antioxidant capabilities. It is shown that pullulan hydrogels are an effective cell delivery system and improve mesenchymal stem cell survival and engraftment in high-oxidative-stress environments. The results suggest that glucan hydrogel systems may prove beneficial for progenitor-cell-based approaches to skin regeneration.