Synthesis and Thermotropic Properties of Twin Mesogens Containing a Polymethylene Spacer

DSC and microscopic data are presented for a thermotropic twin mesogen series. Deviations from normal trends were observed.     

Characterization of a laser-induced plasma by spatially resolved spectroscopy of neutral atom and ion emissions.: Comparison of local and spatially integrated measurements

The local values of the parameters that characterize a laser-induced plasma (temperature, electron density, relative number densities of neutral atoms and ions) have been obtained by spatially resolved emission spectroscopy, including the deconvolution of the measured intensity spectra. The plasma has been generated using a Nd:YAG laser with a Fe–Ni alloy in air at atmospheric pressure, and the emission in the time window 3.0–3.5 μs has been detected. The temperature values obtained from neutral atom and ion emissions have been compared in the cases of local and spatially-integrated measurements. Local Boltzmann and Saha–Boltzmann plots with high correlation to linear fittings have been obtained using two broad sets of optically thin neutral atom and ion lines (21 Fe I lines and 15 Fe II lines), resulting in local values of the electronic temperature that coincide within the error. These results of local measurements contrast with those of spatially integrated measurements, for which two different temperatures are obtained from the Boltzmann plots of neutral atoms (9100±150 K) and ions (13 700±300 K). This difference is explained according to the measured distributions of the electronic temperature and the neutral atom and ion number densities, that result in separated emissivity (or population) distributions of neutral atom and ion lines, leading to different neutral atom and ion apparent temperatures (population-averages of the local electronic temperature). Local values of the plasma parameters have been obtained at all the positions with significant emission, including the determination of the electronic temperature from Saha–Boltzmann or Boltzmann plots. The ionization degree is high- and low-varying at the inner part of the plasma, decaying only near the plasma front. The maximum of the ion density does not coincide with the temperature maximum; on the contrary, the axial variation of both the neutral atom and ion densities (that decrease towards the sample surface) is opposite to that of the temperature, a behaviour that is interpreted to result from the plasma expansion process.     

Synthesis and photoinitiated polymerization of diacrylate derivates of halobenzoates

The synthesis, characterization, mesomorphism and photoinitiated polymerization of new thermotropic derivatives of bis{4-[6-(acryloyloxy)hexyloxy]halobenzoate}-1,4-phenylene were studied. Halogen incorporation in the mesogenic unit decreases the stability of the mesophases of monomers containing three aromatic rings. The monomer MIII exhibits a nematic phase which has been macroscopically oriented by surface pre-treatment and fixed by photopolymerization in situ, yielding a uniaxially crosslinked network. The molecular ordering of liquid crystalline diacrylate films was visualized by examining the fracture surface by scanning electron microscopy. These films exhibit a fine texture, illustrating the presence of an oriented layered structure.     

Weak solutions for time‐dependent boundary integral equations associated with the bending of elastic plates under combined boundary data

The existence, uniqueness, stability, and integral representation of distributional solutions are investigated for the equations of motion of a thin elastic plate with a combination of displacement and moment‐stress components prescribed on the boundary. Copyright © 2004 John Wiley & Sons, Ltd.