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[en] The features of changes in the crystal structure and the radiation-chemical transformation of polymer macromolecules irradiated with high-energy particles (accelerated ions), as well as track-etching patterns and the obtainment of track membranes, are examined.
[en] Highlights: • Extends constraint for particle conservation to recent Linear Source (LS) MOC. • LS MOC anisotropic sources with spatially-linear zeroth-order angular moments. • Isotropic source with direction-independent quantities respects particle balance. • Anisotropic sources with direction-dependent quantities respects particle balance. • Numerical results verify particle conservation for isotropic and anisotropic sources. - Abstract: Particle conservation, otherwise known as particle balance, is one of the main properties to examine when considering any transport discretization. In the past, particle conservation has been examined for the ‘Flat Source’ (FS) approximation used in the Method of Characteristics (MOC) for isotropic and anisotropic sources. The work presented here extends one of the necessary constraints for particle conservation to the recent ‘Linear Source’ (LS) approximation in the MOC for isotropic and anisotropic sources. As a result, direction-dependent track renormalization and centroids are examined. A new LS MOC set of equations is derived for problems involving anisotropic sources in which the zeroth-order angular moment of the source possesses spatially-linear expansion coefficients and satisfies particle conservation if direction-dependent track renormalization and centroids are employed. Numerical results are presented which verify that the FS and LS MOC satisfy particle conservation for problems involving isotropic and anisotropic sources by considering a simple pin cell test problem. In addition, results from a set of full-core eigenvalue calculations, which make use of the anisotropic source option, are presented and compared to evaluate the impact of using either direction dependent or direction independent track renormalization (and centroids).
[en] The flying focus is a technique in which a chirped laser beam is focused by a chromatic lens to produce an extended focal spot within which laser intensity can propagate at any velocity. If the intensity is above the ionization threshold of a background gas, an ionization wave will track the ionization threshold intensity isosurface as it propagates. We report on the demonstration of such ionization waves of arbitrary velocity. Subluminal and superluminal ionization fronts were produced, both forward- and backward-propagating relative to the ionizing laser. In conclusion, all backward and all superluminal cases mitigated the issue of ionization-induced refraction that typically challenges the formation of long, contiguous plasma channels.
[en] Unconventional superconductivity typically is closely related to the suppression of ordered states which possibly compete or coexist with superconductivity in the underdoped region. The overdoped systems are usually assumed to stay in a rather conventional Fermi liquid state. However, for iron-based superconductors, experiments indicate that the heavily hole-doped end-member KFeAs, together with its sister compounds, are more complicated including the possibility of emerging electronic nematic order. We present elasto-resistivity measurements of KFeAs, revealing a divergent nematic susceptibility. The evolution of nematic susceptibility is also tracked with isovalent doping and electron doping on the K site. Our results point to unexpected nematic critical point(s) in those overdoped superconductors.
[en] We use the Nernst coefficient to track the nematic fluctuations through the Co-doped phase diagram of LaFeAsO. Similarly to our previous measurements in an 122-iron based superconductor system, we obtain a significant enhancement of the signal in the nematic fluctuation regime. The doping dependence of the Nernst coefficient exhibits a non-monotonic behavior featuring a local maximum in the vicinity of optimal doping. This peculiar doping dependence is also in agreement with our theoretical prediction and hence demonstrates the universality of the sensitivity of the Nernst effect on nematic fluctuations in iron based superconductors.
[en] This paper presents a methodology for optimizing pre-calculated collision-free paths of differential-drive wheeled robots. The main advantage of this methodology is that optimization is done by considering the kinematics and mechanical constraints of the mobile robot. In accordance to this proposal, the optimized path is achieved by applying recursively a local smoothing on an initial path which is originally modeled as a one-dimensional piecewise linear function. By this recursive smoothing, it can be ensured that the original piecewise linear function can be transformed into a smooth one that fulfill the constraints established by the kinematic equations of the wheeled mobile in terms of a minimum radius of curvature. As a result of this, a trajectory which guarantees lower power consumption and lower mechanical wear, is obtained. To show the better performance of the proposed approach, numerical simulation results are contrasted to those obtained from other reported methods with regards to path length, minimum radius of curvature, cross track error, continuity and resulting acceleration.
[en] 2D modular ray tracing algorithms for the solution of neutron transport via the method of characteristics (MOC) is developed and implemented in the Shiraz University Integrated Advanced Neutron Transport Simulator (SAINTS) code. In SAINTS, a flexible modular cyclic ray tracing which produces track information in a combinatorial geometry is developed. To validate the code, C5G7 standard benchmark is used to calculate multiplication factor and pin powers. Comparison of the SAINTS results with the reference data from NEA C5G7 benchmarks indicates a good agreement and acceptable execution time. SAINTS could achieve 10−4 with S6 and 0.1 cm track spacing in 41 min execution time. The maximum and minimum pin powers obtained by SAINTS for C5G7 core are also in good comparison with the reference data from NEA.
[en] Highlights: • Calibration standards are prepared from filter paper to mimic plant tissues. • Assessment of boron concentration in dried plant tissues is confirmed by ICP-MS. • A mathematical method improves the LOD and visual contrast image. • Boron was imaged and quantified in maize leaves and tiny tassel meristems. - Abstract: Quantitative neutron capture radiography (QNCR) of 10B found in pre-dried maize samples has been conducted. Calibration standards constructed from filter paper mimicked plant tissues to reduce confounding matrix effects. A mathematical track elimination method improves the LOD as well as the visual contrast image at low boron concentration levels. The LOD for total boron is 1.7 µg/g in a 4 mm2 region of interest (ROI). The w(B) in five individual maize tassel meristems has been determined to be 14.9 µg/g – 21.2 µg/g.
[en] In nanodosimetry, the ionization component of charged particle track structure is characterized by measuring the frequency distribution of ionizations in target volumes that simulate nanometric sites in liquid water. For the Ion Counter nano-dosimeter at PTB, the sensitive volume is defined by the electrical field and the extraction aperture. In this paper, a procedure is presented to define a cylindrical effective measurement target based on the second moments of the detection efficiency map. An analytical model of the efficiency map is developed to investigate the dependence of the simulated site size on the nano-dosimeter's operating parameters. Within the limits of the simplifying assumptions, the model gives a reasonable approximation of the efficiency map. (authors)
[en] Large unsegmented liquid scintillator detectors play a key role in modern neutrino physics. Event start time and position are essential parameters for the MeV energy range and usually are determined with a vertex reconstruction. On the other hand, for events in the GeV range, vertex reconstructions have been neglected. But in the case of more sophisticate high energy track reconstructions a vertex determination can provide important initial parameters. In this talk a vertex reconstruction applicable for MeV events and GeV events is introduced. It was developed for the LENA detector, but can be used with any unsegmented liquid scintillator detector and no prior knowledge of the event is needed. The basic idea of this vertex reconstruction and preliminary results are discussed.