The Effects of Air and Helium on the Performance of the Ion Trap Detector When Used for Real-Time Monitoring of Some Atmospheric Pollutants

The feasibility of using an ion trap detector for real-time monitoring of volatile organic compounds in atmospheric samples is demonstrated. Detection limits in the low part-per-million to low part-per-billion ranges are achieved with an operating dynamic range of at least 5 orders of magnitude. Sample introduction through semipermeable membranes and molecular leak valves was evaluated. The membrane introduction method provided detection limit enhancements of 10–300 times over the molecular leak method. The effects of partial pressure from air and helium buffer gas were studied, and it was determined that, for optimum amounts of air, the helium buffer gas had no apparent effect on sensitivity or resolution. Air acts as the buffer gas to enhance ion signals by collisionally damping ion motion. The enhancement of molecular ion abundance at high partial pressures of air is postulated to be due to charge exchange and possibly collisional stabilization reactions.     

Comparison of phantom materials for use in quality assurance of microbeam radiation therapy

Microbeam radiation therapy (MRT) is a promising radiotherapy modality that uses arrays of spatially fractionated micrometre‐sized beams of synchrotron radiation to irradiate tumours. Routine dosimetry quality assurance (QA) prior to treatment is necessary to identify any changes in beam condition from the treatment plan, and is undertaken using solid homogeneous phantoms. Solid phantoms are designed for, and routinely used in, megavoltage X‐ray beam radiation therapy. These solid phantoms are not necessarily designed to be water‐equivalent at low X‐ray energies, and therefore may not be suitable for MRT QA. This work quantitatively determines the most appropriate solid phantom to use in dosimetric MRT QA. Simulated dose profiles of various phantom materials were compared with those calculated in water under the same conditions. The phantoms under consideration were RMI457 Solid Water (Gammex‐RMI, Middleton, WI, USA), Plastic Water (CIRS, Norfolk, VA, USA), Plastic Water DT (CIRS, Norfolk, VA, USA), PAGAT (CIRS, Norfolk, VA, USA), RW3 Solid Phantom (PTW Freiburg, Freiburg, Germany), PMMA, Virtual Water (Med‐Cal, Verona, WI, USA) and Perspex. RMI457 Solid Water and Virtual Water were found to be the best approximations for water in MRT dosimetry (within ±3% deviation in peak and 6% in valley). RW3 and Plastic Water DT approximate the relative dose distribution in water (within ±3% deviation in the peak and 5% in the valley). PAGAT, PMMA, Perspex and Plastic Water are not recommended to be used as phantoms for MRT QA, due to dosimetric discrepancies greater than 5%.     

Controlled Synthesis of Large Single Crystals of Metal-Organic Framework CPO-27-Ni Prepared by a Modulation Approach: In situ Single-Crystal X-ray Diffraction Studies

The size of single crystals of the metal-organic framework CPO-27-Ni was incrementally increased through a series of modulated syntheses. A novel linker modulated synthesis using 2,5-dihydroxyterephthalic acid and the isomeric ligand 4,6-dihydroxyisophthalic acid yielded large single crystals of CPO-27-Ni (∼70 μm). All materials were shown to have high crystallinity and phase purity through powder X-ray diffraction, electron microscopy methods, thermogravimetry, and compositional analysis. For the first time single-crystal structure analyses were carried out on CPO-27-Ni. High BET surface areas and nitric oxide (NO) release efficiencies were recorded for all materials. Large single crystals of CPO-27-Ni showed a prolonged NO release and proved suitable for in situ single-crystal diffraction experiments to follow the NO adsorption. An efficient activation protocol was developed, leading to a dehydrated structure after just 4 h, which subsequently was NO-loaded, leading to a first NO loaded single-crystal structural model of CPO-27-Ni.     

Research Problems from the BCC21

A collection of open problems, mostly presented at the problem session of the 21st British Combinatorial Conference.     

Quantum-limited noise performance of a mode-locked laser diode

Low-noise operation of a 9-GHz hybridly mode-locked laser diode is demonstrated. The integrated timing jitter was 47 fs (10 Hz to 10 MHz) and 86 fs (10 Hz to 4.5 GHz), with a pulse width of 6.7 ps. The noise performance as a function of filter bandwidth and oscillator noise is also addressed.     

Electron density and temperature contour plots from alaser-produced plasma using collective ultraviolet Thomson scattering

Temporally integrated ultraviolet collective Thomson scattering measurements were performed with frequency-quadrupled Nd:YAG laser radiation on an underdense long-scalelength aluminum plasma (n_c ~10²¹ cm^-3, Z≈7, T_e≈T_i ⩾50 eV, L⩾100 μm). The plasma was preformed by an Nd:YAG fundamental beam (1.06 μm) with focusable intensities of 10 ¹¹ W/cm². Color images of two-dimensional (2-D) spatially resolved (30 μm) electron density and electron temperature were obtained. These are the shortest wavelength Thomson scattering measurements on a plasma to date     

Polymerabwandlung und Synthese mit Sulfenylderivaten. 5. Mitt. Addukte mit cis-1,4-Polybutadien

Ohne Zusammenfassung     

A theoretical approach to the role of transfer reactions in the thermal decomposition of polymers

The relative importance of intermolecular and intramolecular transfers is investigated in the thermal degradation of polymers, in particular polystyrene.It is indicated that any mechanism for the pyrolysis behaviour of this polymer must include both modes of transfer. The model is offered as a diagnostic tool for mechanistic investigations of the thermal decompositions of polymers.