[en] Large amplitude, turbulent Alfvénic fluctuations have been commonly observed in the solar wind since the first in situ measurements. An important but still unexplained property of such nonlinear fluctuations seen typically in the fastest streams is that, despite the large excursion of the magnetic field fluctuations, the magnitude of the total magnetic field remains nearly constant, a condition that corresponds to spherical polarization. How is this Alfvénic turbulent state achieved in the solar wind remains a fundamental open question in space physics. Although nonlinear Alfvénic fluctuations have been studied for several decades, most of previous work has considered a plasma in thermodynamic equilibrium. The solar wind however displays many non-thermal features and here we discuss how non-thermal effects, in particular pressure anisotropy, and nonlinearities affect the stability and nonlinear evolution of Alfvénic fluctuations with constant total magnetic field magnitude in different plasma-β regimes. (paper)

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[en] Interferometrically-measured wave-lengths of 109 lines of neutral Kr⁸⁴ are compared with those of Kr⁸⁶. Sixty energy levels of neutral Kr⁸⁴ derived from those wavelengths and 25 Kr⁸⁶-Kr⁸⁴ isotope shifts previously measured are given along with their shifts from the energy levels of Kr⁸⁶. Twenty levels of each of Kr⁸², Kr⁸⁰, and Kr⁷⁸ are also evaluated using isotope-shift information in the literature. The differences between the experimentally observed shifts and the normal mass shift leave large negative residuals which are accounted for by ionization energy differences and by the specific mass shift. It appears that the volume effect causes only a very small, if any, energy level shift

[en] In this paper, we propose a novel radiochromic film (RCF)-based computed tomography (CT) dosimetry method, which is different from the method based on CT dose index. RCF dosimetry using Gafchromic QA2 films was performed using two lengths of film-folding phantoms. The phantom was exposed to X-ray CT through a single scan, while the RCF was sandwiched between the phantoms. We analysed the dose profile curve in two directions to investigate the dose distribution. We observed a difference in the dose distribution as the phantom size changed. Our results contradict with the results of previous studies such as Monte Carlo simulation or direct measurement. The ability to visually evaluate 2D dose distributions is an advantage of RCF dosimetry over other methods. This research investigated the ability of 2D X-ray CT dose evaluation using RCF and film-folding phantom. (authors)

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[en] The small High Efficiency pulse tube Cooler (HEC) cooler, that has been produced and flown on a number of space infrared instruments, was originally designed to provide cooling of 10 W @ 95 K. It achieved its goal with >50% margin when limited by the 180 W output ac power of its flight electronics. It has also been produced in 2 stage configurations, typically for simultaneously cooling of focal planes to temperatures as low as 35 K and optics at higher temperatures. The need for even higher cooling power in such a low mass cryocooler is motivated by the advent of large focal plane arrays. With the current availability at NGAS of much larger power cryocooler flight electronics, reliable long term operation in space with much larger cooling powers is now possible with the flight proven 4 kg HEC mechanical cooler. Even though the single stage cooler design can be re-qualified for those larger input powers without design change, we redesigned both the linear and coaxial version passive pulse tube cold heads to re-optimize them for high power cooling at temperatures above 130 K while rejecting heat to 300 K. Small changes to the regenerator packing, the re-optimization of the tuned inertance and no change to the compressor resulted in the increased performance at 150 K. The cooler operating at 290 W input power achieves 35 W@ 150 K corresponding to a specific cooling power at 150 K of 8.25 W/W and a very high specific power of 72.5 W/Kg. At these powers the cooler still maintains large stroke, thermal and current margins. In this paper we will present the measured data and the changes to this flight proven cooler that were made to achieve this increased performance