Absolute band intensities in the nu19/nu23 (530 cm(-1)) and nu7 (777 cm(-1)) bands of acetone ((CH3)2CO) from 232 to 295 K

Absolute band intensities of acetone ((CH3)2CO) in the nu19/nu23 and nu7 band systems near 530 and 777 cm(-1), respectively, were measured at temperatures of 232, 262 and 295 K, using a Fourier transform infrared (FTIR) spectrometer. No evident temperature dependence for the band intensities was observed. The dipole moments and the fundamental band intensities were derived in the harmonic oscillator approximation. The results are useful for the spectroscopic retrieval of acetone concentrations in the upper atmosphere.     

Polycondensation rate of poly(ethylene terephthalate). I. Polycondensation catalyzed by antimony trioxide in presence of reserve reaction

The technique of G. Challa was employed for following the reaction of oligomeric poly(ethylene terephthalate) in the presence of antimony trioxide. This technique is based on determining the changes in glycol and bishydroxyethyl terephthalate concentrations with time at a given temperature. The linear trimer of ethylene terephthalate, prepared from terephthaloyl chloride and bishydroxyethyl terephthalate, was employed as starting material. Rate constants were not corrected for catalyst concentrations. The reaction was studied over the temperature range 221–251°C. The equilibrium constant k_p/k′ for the polycondensation reaction was found to be 0.36. Observed reaction rates were low but faster than in the uncatalyzed reaction studied by Challa. At 231°C. the values of the rate constants found in the presence of 0.025% by weight antimony trioxide were k_p = 0.151.mole^?1 hr.^?1 and k′ = 0.33 l./mole-hr., and the redistribution rate constant was k_R = 0.11 l./mole-hr. From data at four temperatures the estimated activation energies were E_p = 29 kcal. and E_R = 24 kcal. The polycondensation rates were low compared with rates calculated from literature data. A mechanism to explain the difference requires that bishydroxyethyl terephthalate endgroups compete successfully with oligomer endgroups for antimony trioxide catalyst and that the bishydroxyethyl terephthalate catalyst product is unreactive in polymerization.     

Polycondensation rate of poly(ethylene terephthalate). II. Antimony trioxide–catalyzed polycondensation in static thin films on metal surfaces

In the catalyzed polycondensation reaction of poly(ethylene terephthalate), defined by rates of polymerization in thin films under vacuum are orders of magnitude greater than those observed in an equilibrating system. Such behavior is consistent with a mechanism in which a volatile component of the reaction mixture reacts reversibly with the catalyst to render it unreactive in polycondensation; removal of this component is facilitated as polymerizing melt thickness is decreased. In accord with such a mechanism polycondensation rates for polymerizations carried out on metal surfaces at thicknesses of 1 to 5 mils of polymerizing melt are observed to increase with decreasing thickness, provided a catalyst is present. In the absence of a catalyst there is no tendency of rate to increase with decreasing thickness. A number of metal surfaces were found to dissolve in the polymerizing melt. On rhodium and silver, which were found to be inert to such dissolution, uncatalyzed polycondensation rate constants k_p of 0.03 and 0.04 liter mol^?1 min^?1 were found. These values of k_p are low and identical within experimental error. This behavior is in accord with the assumption that no catalysis occurs at the interface of the polymerizing melt and the metal surface. A typical value for the catalyzed rate constant k_p (uncorrected for catalyst concentration) was 0.6 liter mol^?1 min^?1 in a 1-mil thickness of polymerizing melt at 275°C and in the presence of 0.025 wt-% antimony trioxide. The activation energy for the antimony trioxide–catalyzed polycondensation was found to be 14 kcal; for the uncatalyzed polycondensation it was 45 kcal.     

Preparation and crystallographic characterization of a new endohedral,Lu3N@C80.5 (o-xylene), and comparison with Sc3N@C80.5 (o-xylene)

The trimetallic nitride template (TNT) approach has been successfully utilized to prepare the new endohedral Lu(3)N@C(80). Well-ordered crystals of Lu(3)N@C(80).5 (o-xylene) and Sc(3)N@C(80).5 (o-xylene) form upon cooling of o-xylene solutions of these endohedrals and they are isomorphous. Although the positions of the fullerene cage (which is fully ordered and located at a crystallographic center of symmetry) and the o-xylene molecules are nearly identical in these two structures, the positioning of the metal ions in the two crystals differ in significant ways. However, the expected difference in sizes of lutetium and scandium does not affect the dimensions of the C(80) cage. Nevertheless, the positions of the metal atoms do produce a slight outward dislocation of the immediately adjacent carbon atoms.     

Quantitative in-line phase-contrast imaging with multienergy X rays.

We present a new method for quantitative nondestructive characterization of objects by x-ray phase-contrast imaging. Spatial distributions of the projected values of the complex refractive index in the sample are reconstructed by processing near-field images collected at a fixed sample-to-detector distance using a polychromatic incident beam and an energy-sensitive area detector, such as a CCD used in the photon-counting spectroscopy mode. The method has the potential advantages of decreased radiation dose and increased accuracy compared to conventional techniques of x-ray imaging.     

Reproducibility of magnetic resonance imaging measurements of spinal cord atrophy: the role of quality assurance.

A sensitive magnetic resonance imaging (MRI) method to measure spinal cord cross-sectional area with the potential to monitor disease progression has recently been developed. As changes in cord area due to disease are usually small, assessment of the reliability of the methodology is essential in serial studies of spinal cord atrophy. The aim of this study was to institute and evaluate a protocol of quality assurance to determine long-term reproducibility of serial studies. Serial MRI of the spinal cord was carried out in five healthy volunteer controls over 1 year. Cross-sectional spinal cord areas were measured in a total of 46 scans. The mean coefficient of variation of all subjects over one year was 1.35%. The intra-observer coefficient of variation for same scan analysis was 0.63%. This study has confirmed high reliability of our serial data over one year and the on-going quality assurance protocol enables continuing evaluation of the reproducibility of results in serial studies. Quality assurance is an essential and practical component of all serial MRI studies, without which the clinical implications of change cannot be reliably evaluated.     

Thermodynamics‐based modelling of gas chromatography separations across column geometries and systems,including the prediction of peak widths

Thermodynamics‐based models have been demonstrated to be useful for predicting retention time and peak widths in gas chromatography and two‐dimensional gas chromatography separations. However, the collection of data to train the models can be time consuming, which lessens the practical utility of the method. In this contribution, a method for obtaining thermodynamic‐based data to predict peak widths in temperature‐programmed gas chromatography is presented. Experimental work to collect data for peak width prediction is identical to that required to collect data for retention time prediction using approaches that we have presented previously. Using this combined approach, chromatograms including retention times and peak widths are predicted with very high accuracy. Typical errors in retention time are < 0.5%, while errors in peak width are typically < 5% as demonstrated using polycycic aromatic hydrocarbons and a mixture containing compounds with aldehyde, ketone, alkene, alkane, alcohol, and ester functionalities.     

A New Class of Blue‐Emitting Materials for LED Applications: Triarylamine N‐Functionalised 2,7‐Linked Carbazole Polymers

Attachment of triarylamino‐functional groups at the 9‐position of 2,7‐linked carbazole polymers results in blue‐emitting materials with two independent redox processes that were attributed to the triarylamino groups and the polymer backbone, respectively. This new class of blue‐emitting conjugated polymers was prepared via a Suzuki cross‐coupling reaction and showed low turn‐on voltages in electroluminescent devices as a result of their low ionisation potentials. The photophysical, electrochemical and electroluminescent properties of these materials are discussed.

     

Stable suspension of layered double hydroxide nanoparticles in aqueous solution

Seriously aggregated LDH agglomerates can be dispersed by a hydrothermal treatment into homogeneous stable suspensions that contain LDH particles in the range of 50-300 nm.