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.     

ALKALI-LABILE PHOTOLESIONS MAPPING TO PURINE SITES IN ULTRAVIOLET-IRRADIATED DNA

Gel sequencing experiments with the 5'- and 3'-end-labeled oligonucleotides d(A₃GA₄GA₅GA₆GA₃G) and d(AT) ₁₀ have demonstrated that dimeric adenine photoproducts and thymine-adenine photoadducts constitute alkali-labile lesions in UV-irradiated DNA. On treatment with hot piperidine, DNA strand breakage occurs predominantly at the sites of 5'-adenines in the dimeric photoproducts and of 3'-adenines in the thymine-adenine photoadducts. With 5'-end-labeled oligonucleotides of mixed sequence, major UV-induced loci for alkaline cleavage map to purine bases flanked on their 5'-side by two pyrimidines. This behavior does not arise from enhanced photoreactivity of purines in this sequence context as has been inferred from photofootprinting studies. Instead, as shown by 3'-labeling and selective substitution with 5-methylcytosine, it results from the anomalous electrophoretic mobility of 5'-end-labeled fragments produced by alkaline cleavage of DNA at adjacent pyrimidine (6-4) pyrimidone photoproducts.     

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.     

Absolute band intensities of acetone ((CH3)2CO) in the infrared region of 830-3200 cm(-1) at low and room temperatures

Absolute integrated band intensities of acetone (CH3)2CO in the region of 830-3200 cm(-1) have been measured near the temperatures of 233, 260 and 293 K. The spectra were recorded with a Fourier transform infrared (FTIR) spectrometer. The investigated region encompasses a total of 15 fundamental bands. At 293 K, for example, the band intensities range from 16.8 to 554.3 cm(-2) atm(-1) (at 300 K). The intensities have uncertainties of about 5%. All the band intensities increase with decreasing temperature. An empirical formulation was introduced which fit this temperature dependence well and which can be used to predict other unmeasured band intensities in the temperature region of approximately 200-300 K. The 295 K intensities reported here agree to within approximately 10% of previously published values, with lower estimated uncertainties. Low temperature intensity measurements are not available in the literature.     

Laser-excited atomic-fluorescence spectrometry with electrothermal tube atomization

The performance of graphite-tube electrothermal atomizers is evaluated for laser-excited atomic-fluorescence spectrometry for several elements. Three pulsed laser systems are used to pump tunable dye lasers which subsequently are used to excite Pb, Ga, In, Fe, Ir, and Tl atoms in the hot graphite tube. The dye laser systems used are pumped by nitrogen, copper vapour and Nd:YAG lasers. Detection limits in the femtogram and subfemtogram range are typically obtained for all elements. A commercial graphite-tube furnace is important for the successful utilization of the laser-based method when the determination of trace elements is intended, especially when complicated matrices may be present.     

Polycyclooctatetraeneoxy alkane polyanionic polyradicals

The room temperature potassium reduction of 1,2,3-triscyclooctatetraeneoxypropane, in hexamethylphosphoramide (HMPA), yields an anion radical, which disproportionates so strongly to the dianion diradical that the anion radical cannot be observed via EPR. The dianion diradical has one unpaired electron in a primary and one in a secondary ring system, and it can be readily reduced to the corresponding trianion triradical. An analogous reduction of 1,2,3,4-tetrakiscyclooctatetraeneoxybutane does produce an observable anion radical, but it also is readily reduced to the system corresponding to one electron per eight-membered ring (the tetraanion tetraradical). These results and those obtained from systems containing two cyclooctatetraene (COT) moieties are explained in terms of the geometry changes COT undergoes upon one-electron reduction, the interactions between reduced and adjacent unreduced ring systems, and the electron- electron repulsion present in the polyanion polyradicals.     

Mass spectral evidence of alkali metal insertion into C60-cyclooctatetraene complexes: M+@C60-C8H 8 *3-

C60 can be reduced to its trianion anion radical in hexamethylphosphoramide with potassium or cesium metal. The addition of water to these solutions, followed by toluene extraction, yields materials that exhibit the expected mass spectral peaks for the Birch reduction products of C 60 *3- (C60Hn). However, when cyclooctatetraene (COT) is present in the solution, the mass spectral signature for the Birch reduction products of M+@C60-COT*3- and C60-COT*3- are also found. The trianion radical of C60 reacts with COT in HMPA to yield a [2 + 2] cycloaddition product, and subsequent ring opening provides a passageway for the Cs+ or K+ counterion to the interior of the fullerene. Analogous results are not observed when the smaller metals (Na and Li) are used as the reducing agents. Only the larger alkali metal cations form tight ion pairs with the trianion of C60-COT. The tight ion association is necessary to bring the cation into a sufficiently close proximity to the trianion for the cation to proceed to the interior.     

Operational Research and Corporate Planning in Railway Management

The current corporate planning process in Westrail is described and the roles played by operational research and mathematical modelling identified. They do not include forecasting the future. Instead of the "predict and prepare paradigm" a planning approach that tries to design the future has been adopted. The organisation is described in terms of how it has evolved, what it now is, and the key features of its environment. The three stages of planning are described-strategic, tactical and operational. These provide the means for management control of the railway. Environmental assessments linked to goal setting activities are incorporated within the planning process. The significance of operational research in planning, in particular mathematical modelling, is also described. Instead of finding problems to which existing techniques can be applied, O.R. is used to provide effective operational and planning systems as a means of assisting management to design the future for the organisation.     

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.     

Preclinical radiotherapy at the Australian Synchrotron's Imaging and Medical Beamline: instrumentation,dosimetry and a small‐animal feasibility study

Therapeutic applications of synchrotron X‐rays such as microbeam (MRT) and minibeam (MBRT) radiation therapy promise significant advantages over conventional clinical techniques for some diseases if successfully transferred to clinical practice. Preclinical studies show clear evidence that a number of normal tissues in animal models display a tolerance to much higher doses from MRT compared with conventional radiotherapy. However, a wide spread in the parameters studied makes it difficult to make any conclusions about the associated tumour control or normal tissue complication probabilities. To facilitate more systematic and reproducible preclinical synchrotron radiotherapy studies, a dedicated preclinical station including small‐animal irradiation stage was designed and installed at the Imaging and Medical Beamline (IMBL) at the Australian Synchrotron. The stage was characterized in terms of the accuracy and reliability of the vertical scanning speed, as this is the key variable in dose delivery. The measured speed was found to be within 1% of the nominal speed for the range of speeds measured by an interferometer. Furthermore, dose measurements confirm the expected relationship between speed and dose and show that the measured dose is independent of the scan direction. Important dosimetric parameters such as peak dose, valley dose, the collimator output factor and peak‐to‐valley dose ratio are presented for 5 mm × 5 mm, 10 mm × 10 mm and 20 mm × 20 mm field sizes. Finally, a feasibility study on three glioma‐bearing rats was performed. MRT and MBRT doses were prescribed to achieve an average dose of 65 Gy in the target, and magnetic resonance imaging follow‐up was performed at various time points after irradiation to follow the tumour volume. Although it is impossible to draw conclusions on the different treatments with such a small number of animals, the feasibility of end‐to‐end preclinical synchrotron radiotherapy studies using the IMBL preclinical stage is demonstrated.