Relative dosimetry in a 1.5 T magnetic field: an MR-linac compatible prototype scanning water phantom.

The MR-linac is a hybrid MRI radiotherapy system allowing dose delivery in a 1.5 T magnetic field. This paper presents the design and performance of a prototype MR-linac compatible scanning water phantom. Since a scanning water phantom requires dose detectors, the performance air-filled ionization chambers in the magnetic field was characterized. We have found that the linearity and reproducibility of an ionization chamber are unaffected by the magnetic field. Also, moving the ionization chambers in a magnetic field during irradiation does not affect the dose response. When scanning in-plane profiles, the change in irradiation orientation can influence the ionization chamber dose response by up to 0.4%. However this effect can be eliminated by rotating the ionization chamber by 90° before measuring the in-plane profile. The performance of the total scanning water phantom was validated at a clinical setup in a 0 T magnetic field. There was no significant difference between the dose profiles measured with a standard clinical scanning water phantom and the profiles measured with the MR-linac compatible scanning water phantom. The performance of the MR-linac scanning water phantom in the MR-linac was validated using Gafchromic EBT2 film. There was no significant difference in dose profiles between the MR-linac scanning water phantom and the radiochromic film. These results indicate that automated scanning water phantom measurements using ionization chamber detectors are possible in the MR-linac.

Utilization of photon orbital angular momentum in the low-frequency radio domain.

We show numerically that vector antenna arrays can generate radio beams that exhibit spin and orbital angular momentum characteristics similar to those of helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (< or = 1 GHz), digital techniques can be used to coherently measure the instantaneous, local field vectors and to manipulate them in software. This enables new types of experiments that go beyond what is possible in optics. It allows information-rich radio astronomy and paves the way for novel wireless communication concepts.

Biosurfactant yields and nutrient consumption of Pseudomonas fluorescens 378 studied in a microcomputer controlled multifermentation system.

Production of biosurfactant AP-6 and consumption of carbon (succinic acid) and nitrogen (ammonium ions) by Pseudomonas fluorescens 378 were studied under different growth conditions. The study was performed in a microcomputer controlled multibatch fermentation system which enabled simultaneous running of 10 fermentors. The fermentors were mantled glass vessels, temperature controlled by circulated water, and mixing was arranged by magnetic stirrers. They were connected to the computer system (pH measurement and control) via signal conditioning cards. The microcomputer had a 128 kbytes RAM, two 800-kbyte floppy disc drives, a graphic terminal, and expansion cards. Biosurfactant production was independent of the carbon-to-nitrogen ratio and the phosphorus content in the medium. Omitting the Fe(III) supplement to the medium increased the product yield by 120%. Changes in oxygen transfer rate and pH in the iron deficient cultures did not have any effect on the product yield. Iron deficiency increased the cell consumption of carbon source. Consumption of carbon source in relation to nitrogen uptake (carbon/nitrogen quotient) increased with increasing quotient in the growth medium. The uptake of carbon and nitrogen changed in the intervals of 1.2-1.5 g/g biomass and 0.09-0.16 g/g biomass, respectively. The consumption of carbon increased from 1.5 g/g biomass to 2.0 g/g biomass when the medium concentration of phosphorus was decreased from 0.18 to 0.027 g/L.