Nejdůležitější publikace 2. období (CHEMISTRY)

Nejdůležitější odborné publikace vydané během druhého období (do 31. září 2019). Seznam všech publikací výzkumného programu CHEMISTRY vydaných v rámci projektu CAAS najdete na zvláštní stránce, seznam nejdůležitějších publikací za první období pak zde.

Prebiotic synthesis initiated in formaldehyde by laser plasma simulating high-velocity impacts
M. Ferus, F. Pietrucci, A. M. Saitta, O. Ivanek, A. Knizek, P. Kubelík, M. Krus, L. Juha, R. Dudzak, J. Dostál, A. Pastorek, L. Petera, J. Hrncirova, H. Saeidfirozeh, V. Shestivská, J. Sponer, J. E. Sponer, P. Rimmer, S. Civiš and G. Cassone
Astronomy & Astrophysics, Volume 626, June 2019, Article Number A52, Section Atomic, molecular, and nuclear data
Published online 12 June 2019
Context. It is well known that hydrogen cyanide and formamide can universally be considered as key molecules in prebiotic synthesis. Despite the fact that formamide has been detected in interplanetary and interstellar environments, other prebiotic species are far more abundant, including, for example, formaldehyde. However, several results indicate that formamide can play the role of important intermediate as well as that of a feedstock molecule in chemical abiogenesis. Diverse recently proposed scenarios of the origins of the first biopolymers show that liquid formamide environments could have been crucial for the formation of nucleobases, nucleosides, and for phosphorylation reactions, which lead to nucleotides.
Aims. Here we report on a wide exploration of the formaldehyde reaction network under plasma conditions mimicking an asteroid descent in an Earth-like atmosphere and its impact.
Methods. Dielectric breakdown using a high-power kJ-class laser system (PALS – Prague Asterix Laser System) along with quantum mechanical, ab initio molecular dynamics, and enhanced sampling simulations have been employed in order to mimic an asteroid impact plasma.
Results. Being more abundant than formamide both in interstellar and interplanetary environments, during the era of early and late heavy bombardment of Earth and other planets, formaldehyde might have been delivered on asteroids to young planets. In the presence of nitrogen-bearing species, this molecule has been reprocessed under plasma conditions mimicking the local environment of an impacting body. We show that plasma reprocessing of formaldehyde leads to the formation of several radical and molecular species along with formamide.
Conclusion. All the canonical nucleobases, the simplest amino acid (i.e., glycine), and the sugar ribose, have been detected after treatment of formaldehyde and nitrogen gas with dielectric breakdown. Our results, supported by quantum mechanical and enhanced sampling simulations, show that formaldehyde – by producing inter alia formamide – may have had the role of starting substance in prebiotic synthesis.

Recycling of isotopically modified molybdenum from irradiated CerMet nuclear fuel: part 1—concept design and assessment
Kamil Vavřinec Mareš & Jan John
Journal of Radioanalytical and Nuclear Chemistry volume 320, pages 227–233 (2019)
Published: 23 February 2019
This paper deals with concept design and assessment of a process for the recovery of isotopically modified molybdenum from irradiated nuclear CerMet fuels containing the transuranium element oxides in a metallic molybdenum matrix. The recovery of isotopically modified Mo should enable re-use of this valuable resource especially in the case of uranium-free fuels/targets for accelerator-driven transmuters. The process concept proposed is a modification of the standard hydrometallurgical way of molybdenum processing. Further, the most significant expected radionuclidic impurities in the molybdate raffinate were predicted. Separation of these impurities from the concentrated molybdate solution will be described in the following parts of this mini-series.

 

Nejdůležitější publikace 2. období (IRMA)

Nejdůležitější odborné publikace vydané během druhého období (do 31. září 2019). Seznam všech publikací výzkumného programu MATE vydaných v rámci projektu CAAS najdete na zvláštní stránce, seznam nejdůležitějších publikací za první období pak zde.

The effects of swift Xe ion bombardment on the amorphous structure of a VITROPERM type alloy
Š. Michalik, M. Cesnek, M. Pavlovič, M. Miglierini
Journal of Alloys and Compounds, Volume 795, 30 July 2019, Pages 69-78
Influence of swift Xe ion irradiation (ion energy of 11.1 MeV/u, ion fluences from 2.5 × 1012 to 1.0 × 1013 ions/cm2) on the local structural arrangement of a VITROPERM alloy is investigated using synchrotron-based X-ray diffraction, Fe and Nb K-edge X-ray absorption spectroscopy, and 57Fe Mössbauer spectroscopy techniques. The obtained data show an increase of structural disordering due to ion bombardment. However, no alterations in pairwise interatomic lengths are observed. The irradiation-induced structural modifications can be removed by an appropriate post-irradiation heat treatment. We suggest that the microscopic origin of changes induced by the swift heavy ions could be similar to the structural modifications caused by severe plastic deformation.

X-ray fluorescence mapping as a first-hand tool in disseminated ore assessment: sandstone-hosted U–Zr mineralization
Petr Mikysek, Tomáš Trojek, Noemi Mészárosová,Jiří Adamovič, Marek Slobodník
Minerals Engineering, Volume 141, September 2019, 105840
Analytical capabilities of X-ray fluorescence for 2-dimensional elemental analysis were tested on worldwide-unique sandstone-hosted U–Zr mineralization (Bohemian Cretaceous Basin, Czech Republic), and combined with measured spectral data. The applied approach was aimed at the detection of uranium and zirconium, visualization of their distribution across mineralized lithological units and description of their relationships with associated elements (As, Fe, Nb, Pb, Sr, Ti). The studied samples were low-grade uranium-bearing sediments. Experimental work employed laboratory 2D scanning X-ray fluorescence analyzer with the gold target Mini-X X-ray tube. Maps of U–Zr and other identified elements demonstrated their patchy distribution and a frequent association of the elements with mineral fillings (clay matrix, organic matter or Fe sulfides). A correlation-based analysis was used to verify geochemical coherence between the measured elements. This showed an extremely strong linear dependence (R ≥ 0.90) between U and Zr. In addition, a strong correlation (R ≥ 0.85) between U–Zr and some associated elements (As, Nb ± Fe, Pb, Sr) was confirmed. The efficiency and the limits of X-ray fluorescence mapping were tested by comparison with high-resolution techniques. Non-destructive mapping of large natural samples provided relevant data for further mineralogical study with respect to rapid pre-concentration of the ore material.

Parametrization of a tabletop micro‐XRF system
Žiga Šmit, Radek Prokeš, X-Ray Spectrometry, Volume 48, Issue 6, November/December 2019, Pages 682-690, First published: 20 August 2019
A table‐top micro X‐ray fluorescence apparatus composed of a conventional X‐ray tube with a polycapillary lens and a silicon drift X‐ray detector was parametrized according to an independent parameter approach. The tube bremsstrahlung spectrum was calculated from the Bethe‐Heitler equation, convoluted by the energy distribution of radiating electrons in the target. In this paper, we propose a simple analytical approximation for this energy distribution. An analytical approximation is also proposed for transmission of the lens composed of curved capillaries.

Nejdůležitější publikace 2. období (MATE)

Nejdůležitější odborné publikace vydané během druhého období (do 31. září 2019). Seznam všech publikací výzkumného programu MATE vydaných v rámci projektu CAAS najdete na zvláštní stránce, seznam nejdůležitějších publikací za první období pak zde.

Nanoscale frictional properties of ordered and disordered MoS2
Elisabetta Serpini; Alberto Rota; Sergio Valeri; Egor Ukraintsev; Bohuslav Rezek; Tomas Polcar; Paolo Nicolini
Tribology International; Volume 136, August 2019
The present work aims to understand the sliding of ordered/disordered molybdenum disulfide against itself by combination of nanoscale sliding experiments and atomistic simulations. Tribological experiments were performed using lateral force microscopy with tips covered by a thin sputtered MoS2film. Nanoscale contact area between the MoS2-coated tips and MoS2 samples opened up the possibility for close comparison with classical molecular dynamics simulations. Our simulations replicated well the coefficient of friction obtained by experiments for various contact conditions and shed light on nanoscale sliding of both crystalline and amorphous MoS2. Experimental sliding at humid environment demonstrated detrimental effect of water molecules on friction. However, such effect was much less pronounced when compared to that observed in macroscopic sliding experiments.

Increasing Fatigue Endurance of Hydroxyapatite and Rutile Plasma Sprayed Biocomponents by Controlling Deposition In-Flight Properties
J. Cizek; O. Kovarik; F. Siska; J. Bensch; J. Cupera; M. Matejkova; J. Siegl; T. Chraska; K. A. Khor
ACS Biomater. Sci. Eng. 2019, 5, 4, 1703-1714, Publication Date: March 12, 2019
Three sets of hydroxyapatite and rutile-TiO2 coatings were plasma sprayed onto metallic substrates. The spray parameters of the sets were modified so as to obtain different in-flight temperatures and velocities of the powder particles within the plasma jet (ranging from 1778 to 2385 K and 128 to 199 m s–1, respectively). Fatigue endurance of the coated specimens was then tested. The samples were subjected to a symmetric cyclical bend loading, and the crack propagation was monitored until it reached a predefined cross-section damage. The influence of the coating deposition was evaluated with respect to a noncoated reference set and the in-flight characteristics. Attributed to favorable residual stress development in the sprayed samples, it was found that the deposition of the coatings generally led to a prolongation of the fatigue lives. The highest lifetime increase (up to 46% as compared to the noncoated set) was recorded for the coatings deposited under high in-flight temperature and velocity. Importantly, this was achieved without significantly compromising the microstructure or phase composition of the deposited HA and TiO2 layers.

Microstructural evolution of helium-irradiated 6H–SiC subjected to different irradiation conditions and annealing temperatures: A multiple characterization study
N. Daghbouj; LiB. S.; M. Callisti; H. S. Sen; M. Karlik; T. Polcar
Acta Materialia; Volume 181, December 2019
The microstructural phenomena occurring in 6H–SiC subjected to different irradiation conditions and annealing temperatures were investigated to assess the suitability of 6H–SiC as a structural material for nuclear applications. To this aim, a single crystal of 6H–SiC was subjected to He<sup>+</sup> irradiation at 300 keV with different fluences and at temperatures ranging from 25 to 750 °C. Rutherford backscattering/channeling (RBS/C), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were combined to shed light on the microstructural changes induced by irradiation and subsequent annealing (750 to 1500 °C). At room temperature, amorphization starts to occur at a fluence of 2.5 × 1016 cm−2 (0.66 dpa). On the contrary, amorphization was prevented at high irradiation temperatures and fluences. Furthermore, a thin and highly strained region located around the maximum He concentration (Rp) formed. This region results from the accumulation of interstitial atoms which are driven toward the highly damaged region under the actions of a strain gradient and high temperature. Regardless of the fluence and irradiation temperature, the material stores elastic energy, which leads to the trapping of He in dissimilar defect geometries. For irradiation temperatures below 750 °C, helium was accumulated in bubbles which coarsened after annealing. On the other hand, for an irradiation temperature of 750 °C, helium was trapped in platelets (even for medium fluence), which evolved into a homogeneous dense array of cavities during annealing. DFT calculations show that the bubbles are under high pressure and contribute to developing the overall tensile strain in the single crystal 6H–SiC.

Nejdůležitější publikace 2. období (APPLICATIONS)

Nejdůležitější odborné publikace vydané během druhého období (do 31. září 2019). Seznam všech publikací výzkumného programu APPLICATIONS vydaných v rámci projektu CAAS najdete na zvláštní stránce, seznam nejdůležitějších publikací za první období pak zde.

Assessment from in vivo measurements of thyroid dose due to iodine-131 inhalation when stable iodine has been administered
David Broggio, Pedro Teles, Tomáš Vrba, Volodyumyr B. Berkovskyy
Radiation Measurements, Volume 127, August 2019, 106144
Available online 5 July 2019
Potassium iodide (KI) is a well-known thyroid prophylactic agent that blocks the incorporation of radioactive iodide in the thyroid; it is generally available for oral administration by the population in case of a nuclear release. However, the blockage provided by KI is not 100% effective and therefore activity could still be measured in the thyroid after an intake of radioactive iodine. As a consequence of KI administration the thyroid retention function and the thyroid dose coefficient are modified. To assess the thyroid dose from in vivo measurements these two quantities must be taken into account.
In this work we considered the inhalation of 131-iodine by adult, children (1, 5, 10 years-old) and adolescents (15 years). The effect of KI administration was modelled by a time-dependent blood to thyroid transfer rate coefficient. The model was benchmarked against dose coefficient in the absence of KI and against the protective effect curves depending on KI administration time.
This KI specific model was used to provide correction factors for dose assessment. These multiplicative correction factors apply to a “classical” dose assessment, i.e. a dose assessment based on the ICRP default model that ignores the KI effect. This solution has been preferred since it provides ready to use values avoiding implementing the KI specific model. The correction factors depend on the measurement time and on the KI administration time. They are relatively independent of age and can be described by simple analytic functions. Working examples are provided in this study.
For examples, KI administration 12h before the intake and early in vivo measurements (between 4h and 64h) after the intake give correction factors between 1.2 and 15. For late measurements the correction factors are generally small. If KI has been taken after the intake the correction factors are also generally small, except for very early measurements.

Measurements and Monte Carlo Simulations of 241Am Activities in Three Skull Phantoms: EURADOS-USTUR Collaboration
María López; Pedro Nogueira; Tomas Vrba; Richard Tanner; Werner Rühm; Sergei Tolmachev
Health Physics. 117(2):193–201, AUGUST 2019
Publication Date: August 2019
An international intercomparison was organized by Working Group 7, Internal Dosimetry, of the European Radiation Dosimetry Group in collaboration with Working Group 6, Computational Dosimetry, for measurement and Monte Carlo simulation of 241Am in three skull phantoms. The main objectives of this combined exercise were (1) comparison of the results of counting efficiency in fixed positions over each head phantom using different germanium detector systems, (2) calculation of the activity of 241Am in the skulls, (3) comparison of Monte Carlo simulations with measurements (spectrum and counting efficiency), and (4) comparison of phantom performance. This initiative collected knowledge on equipment, detector arrangements, calibration procedures, and phantoms used around the world for in vivo monitoring of 241Am in exposed persons, as well as on the Monte Carlo skills and tools of participants. Three skull phantoms (BfS, USTUR, and CSR phantoms) were transported from Europe (10 laboratories) to North America (United States and Canada). The BfS skull was fabricated with real human bone artificially labeled with 241Am. The USTUR skull phantom was made from the US Transuranium and Uranium Registries whole-body donor (case 0102) who was contaminated due to an occupational intake of 241Am; one-half of the skull corresponds to real contaminated bone, the other half is real human bone from a noncontaminated person. Finally, the CSR phantom was fabricated as a simple hemisphere of equivalent bone and tissue material. The three phantoms differ in weight, size, and shape, which made them suitable for an efficiency study. Based on their own skull calibration, the participants calculated the activity in the three European Radiation Dosimetry Group head phantoms. The Monte Carlo intercomparison was organized in parallel with the measurement exercise using the voxel representations of the three physical phantoms; there were 16 participants. Three tasks were identified with increasing difficulty: (1) Monte Carlo simulation of the simple CSR hemisphere and the Helmholz Zentrum München high-purity germanium detector for calculating the counting efficiency for the 59.54 keV photons of 241Am, in established measurement geometry; (2) Monte Carlo simulation of particular measurement geometries using the BfS and USTUR voxel phantoms and the Helmholz Zentrum München high-purity germanium detector detector; and (3) application of Monte Carlo methodology to calculate the calibration factor of each participant for the detector system and counting geometry (single or multidetector arrangement) to be used for monitoring a person in each in vivo facility, using complex skull phantoms. The results of both exercises resulted in the conclusion that none of the three available head phantoms is appropriate as a reference phantom for the calibration of germanium detection systems for measuring 241Am in exposed adult persons. The main reasons for this are: (1) lack of homogeneous activity distribution in the bone material, or (2) inadequate shape/size for simulating an adult skull. Good agreement was found between Monte Carlo results and measurements, which supports Monte Carlo calibration of body counters as an alternative method when appropriate physical phantoms are not available and the detector and source are well known.

Nejdůležitější publikace 2. období (THEORY)

Tři nejdůležitější odborné publikace vydané během druhého období (do 31. září 2019). Seznam všech publikací výzkumného programu THEORY vydaných v rámci projektu CAAS najdete na zvláštní stránce, seznam nejdůležitějších publikací za první období pak zde.

On the Pointwise Bishop–Phelps–Bollobás Property for Operators,
Sheldon Dantas, Vladimir Kadets, Sun Kwang Kim, Han Ju Lee, Miguel Martin
Canad. J. Math., to appear
First online: 17.10.2018
We study approximation of operators between Banach spaces X and Y that nearly attain their norms in a given point by operators that attain their norms at the same point. When such approximations exist, we say that the pair (X,Y) has the pointwise Bishop–Phelps–Bollobás property (pointwise BPB property for short). In this paper we mostly concentrate on those X, called universal pointwise BPB domain spaces, such that (X,Y) possesses pointwise BPB property for every Y, and on those Y, called universal pointwise BPB range spaces, such that enjoys pointwise BPB property for every uniformly smooth X. We show that every universal pointwise BPB domain space is uniformly convex and that L_p(𝜇) spaces fail to have this property when p>2. No universal pointwise BPB range space can be simultaneously uniformly convex and uniformly smooth unless its dimension is one. We also discuss a version of the pointwise BPB property for compact operators.

Damage model for plastic materials at finite strains
David Melching, Riccardo Scala, Jan Zeman
ZAMM – Zeitschrift fuer Angewandte Mathematik und Mechanik
First online: 3.7.2019
We introduce a model for elastoplasticity at finite strains coupled with damage. The internal energy of the deformed elastoplastic body depends on the deformation, the plastic strain, and the unidirectional isotropic damage. The main novelty is a dissipation distance allowing the description of coupled dissipative behavior of damage and plastic strain. Moving from time‐discretization, we prove the existence of energetic solutions to the quasistatic evolution problem.

Constant slope, entropy, and horseshoes for a map on a tame graph
Adam Bartoš, Jozef Bobok, Pavel Pyrih, Benjamin Vejnar
Ergodic Theory and Dynamical Systems, to appear
First online: 22.4.2019
We study continuous countably (strictly) monotone maps defined on a tame graph, i.e. a special Peano continuum for which the set containing branch points and end points has countable closure. In our investigation we confine ourselves to the countable Markov case. We show a necessary and sufficient condition under which a locally eventually onto, countably Markov map f of a tame graph G is conjugate to a map of constant slope g. In particular, we show that in the case of a Markov map f that corresponds to a recurrent transition matrix, the condition is satisfied for a constant slope e^h_to(f), where h_to(f) is the topological entropy of f. Moreover, we show that in our class the topological entropy h_to(f)is achievable through horseshoes of the map f.