Purpose
A novel dissolution dynamic nuclear polarization (dDNP) polarizer platform is presented. The polarizer meets a number of key requirements for in vitro, preclinical, and clinical applications.
Method
It uses no liquid cryogens, operates in continuous mode, accommodates a wide range of sample sizes up to and including those required for human studies, and is fully automated.
Results
It offers a wide operational window both in terms of magnetic field, up to 10.1 T, and temperature, from room temperature down to 1.3 K. The polarizer delivers a 13C liquid state polarization for [1‐13C]pyruvate of 70%. The build‐up time constant in the solid state is approximately 1200 s (20 minutes), allowing a sample throughput of at least one sample per hour including sample loading and dissolution.
Conclusion
We confirm the previously reported strong field dependence in the range 3.35 to 6.7 T, but see no further increase in polarization when increasing the magnetic field strength to 10.1 T for [1‐13C]pyruvate and trityl. Using a custom dry magnet, cold head and recondensing, closed‐cycle cooling system, combined with a modular DNP probe, and automation and fluid handling systems, we have designed a unique dDNP system with unrivalled flexibility and performance.
We demonstrate a method for the preparation of hyperpolarized water by dissolution Dynamic Nuclear Polarization at high magnetic field. Protons were polarized at 6.7T and 1.1K to >70% with frequency modulated microwave irradiation at 188GHz. 97.2±0.7% of the radical was extracted from the sample in the dissolution in a two-phase system. 16±1mL of 5.0M H in DO with a polarization of 13.0±0.9% in the liquid state was obtained, corresponding to an enhancement factor of 4000±300 compared to the thermal equilibrium at 9.4T and 293K. A longitudinal relaxation time constant of 16±1s was measured. The sample was polarized and dissolved in a fluid path compatible with clinical polarizers. The volume of hyperpolarized water produced by this method enables angiography and perfusion measurements in large animals, as well as NMR experiments for studies of e.g. proton exchange and polarization transfer to other nuclei.
We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave (SCW) harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found that in helical two-stream electron beams the growth rate of the two-stream instability increases with the beam entrance angle. An SCW with the broad frequency spectrum, in which higher harmonics have higher amplitudes, forms when the frequency of the first SCW harmonic is much less than the critical frequency of the two-stream instability. For helical electron beams the spectrum expands with the increase of the beam entrance angle. Moreover, we obtain that utilizing helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers leads to the improvement of their amplification characteristics, the frequency spectrum broadening in multiharmonic signal generation mode, and the reduction of the overall system dimensions.
The review of the design, principles and operation of artificial composite structures with peculiar electromagnetic properties (metamaterials) is presented. Physical preconditions of metamaterials have been considered in order to explain how exciting properties of such structures can be achieved. A detailed classification scheme and a comparative description of the most proven and wide-used metamaterial structures for microwave technologies have been presented. In addition, the most successful examples of metamaterial application in waveguides, resonators and their derived components as well as in antennas technology have been considered and systematized.
Abstract-We report on the evaluation of Schottky barrier diode GaAs multipliers at cryogenic temperatures. A GaAs Schottky barrier diode model is developed for theoretical estimation of doubler performance. The model is used to predict efficiency of doublers from room to cryogenic temperatures. The theoretical estimation is verified experimentally using a 78 GHz doubler cooled down to 14 K. The observed efficiency improvement due to cooling is approximately 4 % per 100 degrees.
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