136 research outputs found
On the origin of eccentricities among extrasolar planets
Most observed extrasolar planets have masses similar to, but orbits very
different from, the gas giants of our solar system. Many are much closer to
their parent stars than would have been expected and their orbits are often
rather eccentric. We show that some of these planets might have formed in
systems much like our solar system, i.e. in systems where the gas giants were
originally on orbits with a semi-major axis of several au, but where the masses
of the gas giants were all rather similar. If such a system is perturbed by
another star, strong planet-planet interactions follow, causing the ejection of
several planets while leaving those remaining on much tighter and more
eccentric orbits. The eccentricity distribution of these perturbed systems is
very similar to that of the observed extrasolar planets with semi-major axis
between 1 and 6 au.Comment: Accepted for publication in MNRAS Letter
The instability of planetary systems in binaries: how the Kozai mechanism leads to strong planet-planet interactions
In this letter we consider the evolution of a planetary system around a star
inside a wide binary. We simulate numerically the evolution of the planetary
orbits for both co-planar and highly-inclined systems. We find that the Kozai
mechanism operates in the latter case. This produces a highly eccentric outer
planet whose orbit crosses those of some of the inner planets. Strong
planet-planet interactions then follow resulting in the ejection of one or more
planets. We note that planetary systems resembling our solar system, formed
around single stars in stellar clusters may exchange into binaries and thus
will be vulnerable to planet stripping. This process will reduce the number of
solar-system like planetary systems, and may produce at least some of the
observed extra-solar planets.Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter
The effects of fly-bys on planetary systems
Most of the observed extrasolar planets are found on tight and often
eccentric orbits. The high eccentricities are not easily explained by
planet-formation models, which predict that planets should be on rather
circular orbits. Here we explore whether fly-bys involving planetary systems
with properties similar to those of the gas giants in the solar system, can
produce planets with properties similar to the observed planets. Using
numerical simulations, we show that fly-bys can cause the immediate ejection of
planets, and sometimes also lead to the capture of one or more planets by the
intruder. More common, however, is that fly-bys only perturb the orbits of
planets, sometimes leaving the system in an unstable state. Over time-scales of
a few million to several hundred million years after the fly-by, this
perturbation can trigger planet-planet scatterings, leading to the ejection of
one or more planets. For example, in the case of the four gas giants of the
solar system, the fraction of systems from which at least one planet is ejected
more than doubles in 10^8 years after the fly-by. The remaining planets are
often left on more eccentric orbits, similar to the eccentricities of the
observed extrasolar planets. We combine our results of how fly-bys effect
solar-system-like planetary systems, with the rate at which encounters in young
stellar clusters occur. For example, we measure the effects of fly-bys on the
four gas giants in the solar system. We find, that for such systems, between 5
and 15 per cent suffer ejections of planets in 10^8 years after fly-bys in
typical open clusters. Thus, encounters in young stellar clusters can
significantly alter the properties of any planets orbiting stars in clusters.
As a large fraction of stars which populate the solar neighbourhood form in
stellar clusters, encounters can significantly affect the properties of the
observed extrasolar planets.Comment: 22 pages, 15 figures, 5 tables. Accepted for publication in MNRA
Close encounters in young stellar clusters: implications for planetary systems in the solar neighbourhood
The stars that populate the solar neighbourhood were formed in stellar
clusters. Through N-body simulations of these clusters, we measure the rate of
close encounters between stars. By monitoring the interaction histories of each
star, we investigate the singleton fraction in the solar neighbourhood. A
singleton is a star which formed as a single star, has never experienced any
close encounters with other stars or binaries, or undergone an exchange
encounter with a binary. We find that, of the stars which formed as single
stars, a significant fraction are not singletons once the clusters have
dispersed. If some of these stars had planetary systems, with properties
similar to those of the solar system, the planets orbits may have been
perturbed by the effects of close encounters with other stars or the effects of
a companion star within a binary. Such perturbations can lead to strong
planet-planet interactions which eject several planets, leaving the remaining
planets on eccentric orbits. Some of the single stars exchange into binaries.
Most of these binaries are broken up via subsequent interactions within the
cluster, but some remain intact beyond the lifetime of the cluster. The
properties of these binaries are similar to those of the observed binary
systems containing extra-solar planets. Thus, dynamical processes in young
stellar clusters will alter significantly any population of solar-system-like
planetary systems. In addition, beginning with a population of planetary
systems exactly resembling the solar system around single stars, dynamical
encounters in young stellar clusters may produce at least some of the
extra-solar planetary systems observed in the solar neighbourhood.Comment: 11 pages, 9 figures, 1 table. Accepted for publication in MNRA
Особенности акушерско-гинекологического консультирования беременных, страдающих эпилепсией
БЕРЕМЕННОСТИ ОСЛОЖНЕНИЯЭПИЛЕПСИ
Association between guidelines and medical practitioners' perception of best management for patients attending with an apparently uncomplicated acute sire throat: a cross-sectional survey in five countries
Objective To investigate the relationship between guidelines and the medical practitioners' perception of optimal care for patients attending with an apparently uncomplicated acute sore throat in five countries (Australia, Germany, Sweden, UK and USA).
Design International cross-sectional survey.
Setting Primary healthcare (PHC).
Participants Medical practitioners working in PHC.
Main outcome measures ORs for: (A) perception of throat swabs as important, (B) perception of blood tests (C reactive protein, B-ESR and B-leucocytes) as important and (C) antibiotic prescriptions if no pathogenic bacteria isolated on throat swab.
Results Guidelines differed significantly; those recommending throat swabs (Sweden and USA) were associated with practitioners perceiving them as important. The UK guideline was the only one actively discouraging the use of throat swabs. Hence, compared with the USA (reference), a throat swab showing no pathogenic bacteria increased the probability of antibiotic prescribing in the UK with OR 3.2 (95% CI 1.7 to 6.1) for adults, whereas it reduced the probability in Sweden for adults OR 0.35 (95% CI 0.13 to 0.96) and children 0.19 (95% CI 0.069 to 0.50).
Conclusions The differences between practitioners' perceptions of best management were associated with their guidelines. It remains unclear if guidelines influenced medical practitioners' perception or if guidelines merely reflect the consensus of current practice. A larger effort should be made to reach an international consensus in high-income countries about the best management of patients attending for an uncomplicated acute sore throat
Leading Learning Networks in Education
This study is one of the main outcomes of Leading Learning by Networking, an Erasmus+ project. It concerns the management of learning networks in schools with regard to the mission of these networks in the context of growing diversity. The text consists of three main parts. The opening chapter is of theoretical study, dealing with the term Professional learning networks and various factors that facilitate this form of collaboration in schools. Attention is also paid to the role of headteachers in the creation of and support for learning networks. The second part is a summary of the results of a qualitative research, which was carried out by means of interviews, aimed at recognition of some aspects of networking in selected schools in the partner countries. Part three describes a range of data obtained from a questionnaire survey on headteachers’ needs and experience in the management of learning networks
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High-dimensional single-cell analysis of human natural killer cell heterogeneity.
Natural killer (NK) cells are innate lymphoid cells (ILCs) contributing to immune responses to microbes and tumors. Historically, their classification hinged on a limited array of surface protein markers. Here, we used single-cell RNA sequencing (scRNA-seq) and cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) to dissect the heterogeneity of NK cells. We identified three prominent NK cell subsets in healthy human blood: NK1, NK2 and NK3, further differentiated into six distinct subgroups. Our findings delineate the molecular characteristics, key transcription factors, biological functions, metabolic traits and cytokine responses of each subgroup. These data also suggest two separate ontogenetic origins for NK cells, leading to divergent transcriptional trajectories. Furthermore, we analyzed the distribution of NK cell subsets in the lung, tonsils and intraepithelial lymphocytes isolated from healthy individuals and in 22 tumor types. This standardized terminology aims at fostering clarity and consistency in future research, thereby improving cross-study comparisons
Genetic Networks Controlling Structural Outcome of Glucosinolate Activation across Development
Most phenotypic variation present in natural populations is under polygenic control, largely determined by genetic variation at quantitative trait loci (QTLs). These genetic loci frequently interact with the environment, development, and each other, yet the importance of these interactions on the underlying genetic architecture of quantitative traits is not well characterized. To better study how epistasis and development may influence quantitative traits, we studied genetic variation in Arabidopsis glucosinolate activation using the moderately sized Bayreuth×Shahdara recombinant inbred population, in terms of number of lines. We identified QTLs for glucosinolate activation at three different developmental stages. Numerous QTLs showed developmental dependency, as well as a large epistatic network, centered on the previously cloned large-effect glucosinolate activation QTL, ESP. Analysis of Heterogeneous Inbred Families validated seven loci and all of the QTL×DPG (days post-germination) interactions tested, but was complicated by the extensive epistasis. A comparison of transcript accumulation data within 211 of these RILs showed an extensive overlap of gene expression QTLs for structural specifiers and their homologs with the identified glucosinolate activation loci. Finally, we were able to show that two of the QTLs are the result of whole-genome duplications of a glucosinolate activation gene cluster. These data reveal complex age-dependent regulation of structural outcomes and suggest that transcriptional regulation is associated with a significant portion of the underlying ontogenic variation and epistatic interactions in glucosinolate activation
Epitaxial growth of perovskite oxide films facilitated by oxygen vacancies
The authors would like to thank P. Yudin for valuable discussions, N. Nepomniashchaia for VASE studies, and S. Cichon for XPS analysis. The authors acknowledge support from the Czech Science Foundation (Grant No. 19-09671S), the European Structural and Investment Funds and the Ministry of Education, Youth and Sports of the Czech Republic through Programme ‘‘Research,
Development and Education’’ (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16-019/0000760), and ERA NET project Sun2Chem (E. K. and L. R.). Calculations have been done on the LASC Cluster in the ISSP UL.Single-crystal epitaxial films of technologically important and scientifically intriguing multifunctional ABO3 perovskite-type metal oxides are essential for advanced applications and understanding of these materials. In such films, a film-substrate misfit strain enables unprecedented crystal phases and unique properties that are not available in their bulk counterparts. However, the prerequisite growth of strained epitaxial films is fundamentally restricted by misfit relaxation. Here we demonstrate that introduction of a small oxygen deficiency concurrently stabilizes epitaxy and increases lattice strain in thin films of archetypal perovskite oxide SrTiO3. By combining experimental and theoretical methods, we found that lattice distortions around oxygen vacancies lead to anisotropic local stresses, which interact with the misfit strain in epitaxial films. Consequently, specific crystallographic alignments of the stresses are energetically favorable and can facilitate epitaxial growth of strained films. Because anisotropic oxygen-vacancy stresses are inherent to perovskite-type and many other oxides, we anticipate that the disclosed phenomenon of epitaxial stabilization by oxygen vacancies is relevant for a very broad range of functional oxides.This work is licensed under CC BY, CC BY-NC licenses.Czech Science Foundation (Grant No. 19-09671S); European Structural and Investment Funds and the Ministry of Education, Youth and Sports of the Czech Republic through Programme ‘‘Research, Development and Education’’ (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16-019/0000760), and ERA NET project Sun2Chem; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²
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