Probing Fluorine Interactions in a Polyhydroxylated Environment: Conservation of a C-F center dot center dot center dot H-C Recognition Motif in Presence of O-H center dot center dot center dot O Hydrogen Bonds

Three conformationally locked fluorinated polycyclitols have been specially crafted on a rigid trans-decalin backbone, employing a surprisingly facile pyridine-poly(hydrogen fluoride)-mediated stereospecific epoxide ring opening as the key reaction. Molecula design of the three fluorinated probes under study focused on providing an efficient platform for (a) evaluating the ability of covalently bonded fluorine, vis-a-vis the isosteric hydroxy group, to act as a H-bond acceptor and (b) examining the possibility for an organic fluorine moiety, placed suitably in a spatially invariant position, to engage an 1,3-diaxial OH functionality in a purported intramolecular O-H center dot center dot center dot F hydrogen bond. The present endeavour reveals that C(sp(3))-F center dot center dot center dot H-C(sp(3)) hydrogen bonds, though weak and lesser investigated, can indeed be observed and supramolecular recognition motifs, involving such interactions, can be conserved even in crystal structures laden with stronger O-H center dot center dot center dot O hydrogen bonds.

Application of acoustic emission in drilling of composite laminates

Acoustic emission (AE) technique was used to characterise drilling of composite laminates. Uni-directional glass fibre reinforced plastic (GFRP) laminates consisting of 12-layers and 16-layers (0/90)(s) were drilled using a twist drill and the generated AE was monitored. Results of the investigations reveal that the complexion of the acoustic emission root mean square (AE-RMS) signal response changes from the drill entry to the exit thus giving an overall understanding about the different events that take place during drilling. Also, AE-RMS signal level increases with an increase in the applied thrust and further reveals that it is possible to evaluate the drill induced damages in composites through AE signal characterisation. (C) 2000 Elsevier Science Ltd. All rights reserved.

An NMR study of the coexistence of nematic and “induced” smectic phases in mixtures of nematics

Deuteron NMR studies of mixtures of nematic liquid crystals such as N-(p-ethoxybenzylidene)-p-n-butylaniline and trans-4-pentyl-4-(4-cyanophenyl)cyclohexane and the molecules dissolved therein show the coexistence of up to three different spectra at certain concentrations and temperatures. This is attributed to the coexistence of nematic and “induced” smectic phases.

Change in spectrum of Brownian fluctuations of optically trapped red blood cells due to malarial infection

We study the properties of single red blood cells (RBCs) held in an optical-tweezers trap. We observe a change in the spectrum of Brownian fluctuations between RBCs from normal and malaria-infected samples. The change, caused by infection-induced structural changes in the cell, appears as a statistical increase in the mean (by 25%) and standard deviation (by 200%) of the corner frequency measured over similar to 100 cells. The increase is observed even though the ensemble of cells being measured consists mostly of cells that do not actually host the parasite, but are from an infected pool. This bystander effect appears to vindicate other observations that infected cells can affect the biomechanical properties of uninfected cells. The change is also observed to be independent of the stage of infection and its duration, highlighting its potential for disease detection. (C) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3427142].

Ordering near the percolation threshold in models of two-dimensional interacting bosons with quenched dilution

Randomly diluted quantum boson and spin models in two dimensions combine the physics of classical percolation with the well-known dimensionality dependence of ordering in quantum lattice models. This combination is rather subtle for models that order in two dimensions but have no true order in one dimension, as the percolation cluster near threshold is a fractal of dimension between 1 and 2: two experimentally relevant examples are the O(2) quantum rotor and the Heisenberg antiferromagnet. We study two analytic descriptions of the O(2) quantum rotor near the percolation threshold. First a spin-wave expansion is shown to predict long-ranged order, but there are statistically rare points on the cluster that violate the standard assumptions of spin-wave theory. A real-space renormalization group (RSRG) approach is then used to understand how these rare points modify ordering of the O(2) rotor. A new class of fixed points of the RSRG equations for disordered one-dimensional bosons is identified and shown to support the existence of long-range order on the percolation backbone in two dimensions. These results are relevant to experiments on bosons in optical lattices and superconducting arrays, and also (qualitatively) for the diluted Heisenberg antiferromagnet La-2(Zn,Mg)(x)Cu1-xO4.

Markov random fields and spatial smoothing in improving of forest inventory estimates

Markov random fields (MRF) are popular in image processing applications to describe spatial dependencies between image units. Here, we take a look at the theory and the models of MRFs with an application to improve forest inventory estimates. Typically, autocorrelation between study units is a nuisance in statistical inference, but we take an advantage of the dependencies to smooth noisy measurements by borrowing information from the neighbouring units. We build a stochastic spatial model, which we estimate with a Markov chain Monte Carlo simulation method. The smooth values are validated against another data set increasing our confidence that the estimates are more accurate than the originals.

Combustion of ammonium perchlorate-based composite propellants in presence of methylammonium perchlorates

The effect of tri- and tetramethylammonium perchlorates (MAP-3 and MAP-4) on the burning rate of ammonium perchlorate (AP) based propellants has been determined at various pressures. Both additives increase the burning rate; however, MAP-3 has a moderate effect, whereas MAP-4 has a rather large effect. To explain the results, the thermal decomposition and calorimetric values of the propellants having these additives have been examined. Compound MAP-3 affects the thermal decomposition rate considerably, whereas MAP-4 has virtually no effect on the decomposition rate. The contrasting effects of MAP-4 on decomposition and burning rate suggest that the enhancement of burning rate may be due to the catalysis of gas-phase reactions. Further, detailed differences between behaviour of MAP-3, and MAP-4 appear to be attributable to the melting and low-temperature exotherm of MAP-3 and nonmelting and high-temperature exotherm of MAP-4.

A study of interactions in He2 1 in terms of the electronic forces

The He+He+1 interactions have been studied, as a function of the internuclear separation R, in terms of the electronic forces acting on the nuclei and the change in the charge distribution. The analysis reveals that at large R the atomic densities are polarized inwards, causing an attractive force on each nucleus, while at small R the difference in the nature of the interactions in the 2Σu and 2Σg systems is noted. It is seen that the He+He+1 (2Σu) interaction is less attractive than the He+1+He+1 interaction at lower values of R.

Superconductivity in the 100–120 K region in oxides of the Tl-Ca-Ba-Cu-O system

Oxides with different cation ratios 2122, 2212, 2213 and 2223 in the Ti-Ca-Ba-Cu-O system exhibit onset of superconductivity in the 110–125 K range with zero-resistance in the 95–105 K range. Electron microscopic studies show dislocations, layered morphology and other interesting features. These oxides absorb electromagnetic radiation (9.11 GHz) in the superconducting phase.