Liquid rocket, Diesel or aircraft engines may operate in the transcritical regime. In such thermodynamic conditions, the classical phase change that occurs at subcritical pressure disappears and the ...mixing layer between the dense and cold jet and the outer gaseous stream is characterized by large variations of density and thermodynamic properties. Fluids show strong departure from a perfect gas behavior and a real-gas formulation is needed to model the fluid state. The extension of the unstructured AVBP solver, jointly developed by CERFACS and IFPEN, to handle high-pressure thermodynamics is presented in details. It is then validated on the experimental coaxial injectors studied with the Mascotte test rig from ONERA that operate in the transcritical range, namely the LOx/GH2 cases A60 and C60 and the LOx/GCH4 configuration G2. The flame pattern observed in experiments is properly recovered, hence validating the numerical strategy. Numerical results are then discussed focusing on the role of the momentum flux ratio on the development of transcritical flames.
The climatic cycles with subsequent glacial and intergalcial periods have had a great impact on the distribution and evolution of species. Using genetic analytical tools considerably increased our ...understanding of these processes. In this review I therefore give an overview of the molecular biogeography of Europe. For means of simplification, I distinguish between three major biogeographical entities: (i) "Mediterranean" with Mediterranean differentiation and dispersal centres, (ii) "Continental" with extra-Mediterranean centres and (iii) "Alpine" and/or "Arctic" with recent alpine and/or arctic distribution patterns. These different molecular biogeographical patterns are presented using actual examples. Many "Mediterranean" species are differentiated into three major European genetic lineages, which are due to glacial isolation in the three major Mediterranean peninsulas. Postglacial expansion in this group of species is mostly influenced by the barriers of the Pyrenees and the Alps with four resulting main patterns of postglacial range expansions. However, some cases are known with less than one genetic lineage per Mediterranean peninsula on the one hand, and others with a considerable genetic substructure within each of the Mediterranean peninsulas, Asia Minor and the Maghreb. These structures within the Mediterranean sub-centres are often rather strong and in several cases even predate the Pleistocene. For the "Continental" species, it could be shown that the formerly supposed postglacial spread from eastern Palearctic expansion centres is mostly not applicable. Quite the contrary, most of these species apparently had extra-Mediterranean centres of survival in Europe with special importance of the perialpine regions, the Carpathian Basin and parts of the Balkan Peninsula. In the group of "Alpine" and/or "Arctic" species, several molecular biogeographical patterns have been found, which support and improve the postulates based on distribution patterns and pollen records. Thus, genetic studies support the strong linkage between southwestern Alps and Pyrenees, northeastern Alps and Carpathians as well as southeastern Alps and the Dinaric mountain systems, hereby allowing conclusions on the glacial distribution patterns of these species. Furthermore, genetic analyses of arctic-alpine disjunct species support their broad distribution in the periglacial areas at least during the last glacial period. The detailed understanding of the different phylogeographical structures is essential for the management of the different evolutionary significant units of species and the conservation of their entire genetic diversity. Furthermore, the distribution of genetic diversity due to biogeographical reasons helps understanding the differing regional vulnerabilities of extant populations.
Researchers must make numerous choices when conducting factor analyses, each of which can have significant ramifications on the model results. They must decide on an appropriate sample size to ...achieve accurate parameter estimates and adequate power, a factor model and estimation method, a method for determining the number of factors and evaluating model fit, and a rotation criterion. Unfortunately, researchers continue to use outdated methods in each of these areas. The present article provides a current overview of these areas in an effort to provide researchers with up-to-date methods and considerations in both exploratory and confirmatory factor analysis. A demonstration was provided to illustrate current approaches. Choosing between confirmatory and exploratory methods is also discussed, as researchers often make incorrect assumptions about the application of each.
The combination of high atomic number and high oxidation state in UVI materials gives rise to both high X‐ray attenuation efficiency and intense green luminescence originating from ligand‐to‐metal ...charge transfer. These two features suggest that UVI materials might act as superior X‐ray scintillators, but this postulate has remained substantially untested. Now the first observation of intense X‐ray scintillation in a uranyl–organic framework (SCU‐9) that is observable by the naked eye is reported. Combining the advantage in minimizing the non‐radiative relaxation during the X‐ray excitation process over those of inorganic salts of uranium, SCU‐9 exhibits a very efficient X‐ray to green light luminescence conversion. The luminescence intensity shows an essentially linear correlation with the received X‐ray intensity, and is comparable with that of commercially available CsI:Tl. SCU‐9 possesses an improved X‐ray attenuation efficiency (E>20 keV) as well as enhanced radiation resistance and decreased hygroscopy compared to CsI:Tl.
U are scintillating: The observation of intense X‐ray scintillation in a uranyl‐organic framework is reported. Advances are shown in X‐ray attenuation efficiency (E>20 keV) as well as enhanced radiation resistance and decreased hygroscopy when compared to the commercially available scintillator CsI:Tl.
Europe is characterised by several high mountain systems dominating major parts of its area, and these structures have strongly influenced the evolution of taxa. For species now restricted to these ...high mountain systems, characteristic biogeographical patterns of differentiation exist. (i) Many local endemics are found in most of the European high mountain systems especially in the Alps and the more geographically peripheral regions of Europe. Populations isolated in these peripheral mountain ranges often have strongly differentiated endemic genetic lineages, which survived and evolved in the vicinity of these mountain areas over long time periods. (ii) Populations of taxa with wide distributions in the Alps often have two or more genetic lineages, which in some cases even have the status of cryptic species. In many cases, these lineages are the results of several centres of glacial survival in the perialpine areas. Similar patterns also apply to the other geographically extended European high mountain systems, especially the Pyrenees and Carpathians. (iii) Populations from adjoining high mountain systems often show similar genetic lineages, a phenomenon best explained by postglacial retreat to these mountains from one single differentiation centre between them. (iv) The populations of a number of species show gradients of genetic diversity from a genetically richer East to a poorer West. This might indicate better glacial survival conditions for this biogeographical group of species in the more eastern parts of Europe.
Precise detection of low‐dose X‐ and γ‐radiations remains a challenge and is particularly important for studying biological effects under low‐dose ionizing radiation, safety control in medical ...radiation treatment, survey of environmental radiation background, and monitoring cosmic radiations. We report here a photoluminescent uranium organic framework, whose photoluminescence intensity can be accurately correlated with the exposure dose of X‐ or γ‐radiations. This allows for precise and instant detection of ionizing radiations down to the level of 10−4 Gy, representing a significant improvement on the detection limit of approximately two orders of magnitude, compared to other chemical dosimeters reported up to now. The electron paramagnetic resonance analysis suggests that with the exposure to radiations, the carbonyl double bonds break affording oxo‐radicals that can be stabilized within the conjugated uranium oxalate‐carboxylate sheet. This gives rise to a substantially enhanced equatorial bonding of the uranyl(VI) ions as elucidated by the single‐crystal structure of the γ‐ray irradiated material, and subsequently leads to a very effective photoluminescence quenching through phonon‐assisted relaxation. The quenched sample can be easily recovered by heating, enabling recycled detection for multiple runs.
A uranium MOF dosimeter: A photoluminescent uranium–organic framework, whose intensity accurately correlates with the exposure dose of X‐ or γ‐radiations, enables the precise and instant detection of ionizing radiations. The detection limit of 10−4 Gy represents an improvement of approximately two orders of magnitude compared to other chemical dosimeters reported up to now.
The merging of small‐scale syntheses and rapid crystallization methods have provided access to crystalline samples of berkelium (Z=97) and californium (Z=98) coordination complexes and compounds that ...can be interrogated with a suite of spectroscopic tools and structural elucidation approaches that have come online over the last 20 years. The combination of this experimental data with relativistic theoretical methods that capture the effects of spin‐orbit coupling and scalar relativistic effects have allowed us to understand the electronic structure of berkelium and californium compounds at a level of detail that was not previously possible. The harbinger of this new era of post‐curium chemistry was the synthesis and characterization of Cf{B6O8(OH)5}. This compound possesses a structure type that is distinct from earlier actinide borates, a reduction in coordination number for californium, contracted Cf−O bond lengths, a substantially reduced magnetic moment with respect to the calculated free‐ion moment and, most importantly, vibronically coupled broadband photoluminescence. Ligand‐field analysis also showed that the splitting of the ground state was larger than typically found in the f‐block elements, and when taken together places its overall electronic structure as a hybrid of d‐ and f‐block components. The discovery of the unusual properties of this compound has led to the development of large families of 4f and 5f coordination complexes, in an effort to uncover the underlying origin of the electronic structure oddities, and whether there really is a sharp onset of these changes at californium. This in turn pushed the development of far more challenging berkelium chemistry (from a radiologic standpoint) because the half‐life of the isotopes decreases from 351 years for 249Cf to 330 days for 249Bk. This short review details some of the chemistry that has been reported over the last 15 years, and its consequences for understanding the periodic table.
The difference between being early or late is important! Recent investigations of berkelium and californium demonstrates why the later actinides deserve special treatment and should no longer be viewed as “lanthanide‐like”.
Some decades ago, biogeographers distinguished three major faunal types of high importance for Europe: (i) Mediterranean elements with exclusive glacial survival in the Mediterranean refugia, (ii) ...Siberian elements with glacial refugia in the eastern Palearctic and only postglacial expansion to Europe and (iii) arctic and/or alpine elements with large zonal distributions in the periglacial areas and postglacial retreat to the North and/or into the high mountain systems. Genetic analyses have unravelled numerous additional refugia both of continental and Mediterranean species, thus strongly modifying the biogeographical view of Europe. This modified notion is particularly true for the so-called Siberian species, which in many cases have not immigrated into Europe during the postglacial period, but most likely have survived the last, or even several glacial phases, in extra-Mediterranean refugia in some climatically favourable but geographically limited areas of southern Central and Eastern Europe. Recently, genetic analyses revealed that typical Mediterranean species have also survived the Last Glacial Maximum in cryptic northern refugia (e.g. in the Carpathians or even north of the Alps) in addition to their Mediterranean refuge areas.
A new approach to fused helicenes is reported, where varied substituents are readily incorporated in the extended aromatic frame. From the alkynyl precursor, the final helical compounds are obtained ...under mild conditions in a two‐step process, in which the final C−C bond is formed via a photochemical cyclization/ dehydroiodination sequence. The distortion of the π‐system from planarity leads to unusual packing in the solid state. Computational analysis reveals that substituent incorporation perturbs geometries and electronic structures of these nonplanar aromatics.
A new approach to fused helicenes is reported, in which varied substituents are readily incorporated in the extended aromatic frame. From an alkynyl precursor, the final helical compounds are obtained in a two‐step process, in which the final C−C bond is photochemically forged by coupling cyclization and dehydroiodination. The distortion of the π‐system from planarity leads to unusual packing in the solid state.
•Consistent phase-change procedure are proposed and investigated for any interface capturing method.•Accurate and second-order discretizations for diffusion operator with flux jump are ...presented.•Second-order accurate gradients from any interface representation are obtained.•VOF and Level-Set framework for evaporating flows are limited to first-order convergence with important errors in 3D.
In this paper, the modeling of phase change in an incompressible two-phase flow solver is detailed without restricting the numerical methods to a specific interface capturing method. Starting from existing methodologies of the literature, the present work gives a step-by-step investigation of each numerical aspect of phase change to obtain an accurate and consistent solver.
The main challenge when including phase-change is the handling of flux discontinuities at the interface when advancing temperature and species mass fraction. An accurate and second order discretization is proposed for any Eulerian representation of the interface either by adding a sharp source term or by imposing a boundary condition at the interface. As the accuracy and convergence rate of such solver are driven by the reconstruction of the evaporation rate m˙, particular attention is devoted to the reconstruction of gradient normal to the interface. Several methodologies are proposed to compute second-order gradients at the interface location adapted to any interface representation. Applying such techniques to a second-order accurate field leads to an expected first order accuracy of m˙ but with remarkable accuracy improvements using ghost cell methods with quadratic extrapolation. Then, several phase-change procedures are built by combining a selection of numerical methods to handle flux discontinuities and evaluate gradients. The procedures are investigated on planar phase-change simulations to bring out inconsistent combination choices. Finally, a multidimensional evaporation test case is presented to show the final accuracy and limitations of phase-change modeling in today two-phase flow solvers.
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