214 research outputs found
DETERMINATION OF THE PM10 URBAN THRESHOLD VELOCITY OF RE-SUSPENSION IN AN INNER PART OF URBAN AREA
In this paper authors focus on determination of the threshold velocity of re-suspension for particles 10 m in an urban
street canyon with two-way traffic. The urban wind threshold velocity of re-suspension is derived from a long-term measurement
carried out in the city of Brno. A numerical modelling based on the finite volume method is used for a detail study of the relation
between a wind velocity above buildings roofs and an air velocity just above the ground surface. The predicted threshold air velocity
of re-suspension at the bottom part of the studied street canyon is compared with two theoretical studies on particle re-suspension.
Calculations are carried out for perpendicular, longitudinal and oblique (45°) wind direction with and without inclusion of traffic
dynamic. To simulate traffic, an original model developed previously by the authors is used that takes into account traffic density,
speed of cars and number of traffic lanes
Evolution of ferromagnetic and non-Fermi liquid state with doping:the case of Ru doped UCoGe
We have investigated the impact of Ru substitution for Co on the behavior of
the ferromagnetic superconductor UCoGe by performing x-ray diffraction,
magnetization, specific heat and electrical resistivity measurements on
polycrystalline samples of the
series (). The initial Ru substitution up to
leads to a simultaneous sharp increase of the Curie temperature and spontaneous
magnetization up to maximum values of and
per formula unit, respectively, whereas
superconductivity vanishes already for . Further increase of the
Ru content beyond leads to a precipitous decrease of both,
and towards a ferromagnetic quantum critical
point (QCP) at . Consequently the magnetic phase
diagram consists of a well-developed ferromagnetic dome. We discuss the
evolution of ferromagnetism with on the basis of band structure changes due
to varying 5-ligand hybridization. This scenario is supported by the results
of electronic structure calculations and consideration of the simplified
periodic Anderson model. The analysis of the temperature dependencies of the
electrical resistivity and heat capacity at low temperatures of the samples in
the vicinity of the QCP reveals a non-Fermi liquid behavior and assigns the
ferromagnetic quantum phase transition to be most likely of a continuous
Hertz-Millis type.Comment: accepted for publication in PR
THIN NITRIDE LAYERS AS PERMEATION BARRIERS
Permeation barriers represent one of the crucial fields in materials development for thermonuclear fusion. Primary objective of the barriers is to suppress the permeation of hydrogen isotopes (mainly tritium) from future thermonuclear fusion facilities. Secondary objective is to reduce hydrogen retention in structural materials, potentially also improving their corrosion resistance. Expected reactor conditions put high demands on the material, as well as on the final barrier quality. Key properties are tritium permeation reduction, absence of defects (especially cracks), high-temperature stability and corrosion resistance, and compatibility with structural materials (mostly ferritic-martensitic steels). Regarding industrial scale production, ability of the deposition method to coat large complex surfaces is desirable. Thin nitride layers, identified as promising permeation barriers, were prepared by diffusion-based nitridation and physical vapour deposition (PVD) and characterized
Gradual localization of 5f states in orthorhombic UTX ferromagnets - polarized neutron diffraction study of Ru substituted UCoGe
We report on a microscopic study of the evolution of ferromagnetism in the Ru
substituted ferromagnetic superconductor (FM SC) UCoGe crystallizing in the
orthorhombic TiNiSi-type structure. For that purpose, two single crystals with
composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge have been prepared and
characterized by magnetization, AC susceptibility, specific heat and electrical
resistivity measurements. Both compounds have been found to order
ferromagnetically below TC = 6.5 K and 7.5 K, respectively, which is
considerably higher than the TC = 3 K of the parent compound UCoGe. The higher
values of TC are accompanied by enhanced values of the spontaneous moment
mspont. = 0.11 mB/f.u. and mspont. = 0.21 mB/f.u., respectively in comparison
to the tiny spontaneous moment of UCoGe (about 0.07mB/f.u.). No sign of
superconductivity was detected in either compound. The magnetic moments of the
samples were investigated on the microscopic scale using polarized neutron
diffraction (PND) and for UCo0.88Ru0.12Ge also by soft X-ray magnetic circular
dichroism (XMCD). The analysis of the PND results indicates that the observed
enhancement of ferromagnetism is mainly due to the growth of the orbital part
of the uranium 5f moment mL(U), reflecting a gradual localization of the 5f
electrons with Ru substitution. In addition, the parallel orientation of the U
and Co moments has been established in both substituted compounds. The results
are discussed and compared with related isostructural ferromagnetic UTX
compounds (T - transition metals, X - Si, Ge) in the context of a varying
degree of the 5f-ligand hybridization
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