3,031 research outputs found

    Binary stars in young clusters: models versus observations of the Trapezium Cluster

    Full text link
    The frequency of low-mass pre-main sequence binary systems is significantly lower in the Trapezium Cluster than in Taurus-Auriga. We investigate if this difference can be explained through stellar encounters in dense clusters. To this effect, a range of possible models of the well observed Trapezium Cluster are calculated using Aarseth's direct N-body code, which treats binaries accurately. The results are confronted with observational constraints. The range of models include clusters in virial equilibrium, expanding clusters as a result of instantaneous mass loss, as well as collapsing clusters. In all cases the primordial binary proportion is larger than 50 per cent, with initial period distributions as observed in Taurus-Auriga and the Galactic field. It is found that the expanding model, with an initial binary population as in the Galactic field, is most consistent with the observational constraints. This raises the possibility that the primordial group of OB stars may have expelled the cluster gas roughly 50 000 yr ago. The cluster's bulk expansion rate is thus a key observable that needs to be determined. The other models demonstrate that the rapidly decreasing binary proportion, its radial dependence and the form of the period distribution, together with structural and kinematical data, are very useful diagnostics on the present and past dynamical state of a young cluster. In particular, kinematical cooling from the disruption of wide binaries is seen for the first time.Comment: 34 pages, 13 figures, LaTeX, uses own_sngl.sty, accepted by New

    Bibliometrics as a pathway to (future) research strategies. Case study – seeking research excellence

    Get PDF
    Prioritizing quantity of publications over quality by many researchers is an unintended effect of the national evaluation in Czech Republic. Simple journal-level indicators behind the evaluation procedures over-simplify the complex view at research performance. Many research organizations accepted these indicators for internal analysis and assessment of the quality of research. In opposition to this trend, Masaryk University progressed in implementing qualified bibliometrics with professional tools and approaches into decision-making procedures and strategies at all levels. In the poster, we demonstrate sample analyses and their outputs at the Masaryk University, especially the exercise of identifying research excellence and focus areas. We used two approaches. Firstly, “bottom-up” approach, deduction of impactful research topics by analysing citation data in the whole publication record together with a validation of highly cited publications of MU authors in their other production. Besides this, we unsuccessfully tested application of CWTS microfields for identifying impactful topics by pre-defined keywords. As a “top-down” approach, we reviewed and consulted results of our analysis with vice-deans for research before making final decision. Results of both approaches matched very well. Identification of excellent research topics is now being used for official university marketing and web presentation. University environment accepted bibliometrics stepwise as a useful research-supporting tool and accepted emphasis on individual excellence. Important discussions started about research performance and demand for further bibliometric monitoring

    Teleworking in SMEs before the onset of coronavirus infection in the Czech Republic

    Get PDF
    Due to the new information and communication technologies, it is now possible to disconnect work from space and time and to take advantage of new ways of organizing work. One of the options is teleworking (TW), currently being implemented throughout Europe due to the condition created by the coronavirus pandemic. The aim of the paper is twofold: (i) to analyse a range of factors (size of the enterprise; foreign owner; written strategy; project-driven enterprise; disabilities; work-life balance; benefits, lack of workers, illness, lower cost, relax at work and comfort; renting space, IT level) influencing the duration of TW implementation in the small and medium-sized enterprises (SMEs) and (ii) to better define the differences between the SMEs where TW was introduced in a short time, and those introducing it over a longer period. Out of the total of 31 factors, six factors have been proved to have a different impact on the duration of TW implementation (TW implementation due to higher efficiency; monitoring is performed only according to the results; the managers see the disadvantage of TW in its possible misuse; the enterprises use internal TW regulations; the managers see the main advantage as higher operational flexibility; the introduction of TW, due to the balance of work and family life). All together, 44,000 SMEs in the Czech Republic were invited into the research. The data were collected from 1,018 enterprises, with 60% of the enterprises using TW actively; on average, these enterprises have been using it for seven years

    The centre-to-limb variations of solar Fraunhofer lines imprinted upon lunar eclipse spectra - Implications for exoplanet transit observations

    Full text link
    The atmospheres of exoplanets are commonly studied by observing the transit of the planet passing in front of its parent star. The obscuration of part of the stellar disk during a transit will reveal aspects of its surface structure resulting from general centre-to-limb variations (CLVs). These become apparent when forming the ratio between the stellar light in and out of transit. These phenomena can be seen particularly clearly during the progress of a penumbral lunar eclipse, where the Earth transits the solar disk and masks different regions of the solar disk as the eclipse progresses. When inferring the properties of the planetary atmosphere, it is essential that this effect originating at the star is properly accounted for. Using the data observed from the 2014-April-15 lunar eclipse with the ESPaDOnS spectrograph mounted on the Canada France Hawaii Telescope (CFHT), we have obtained for the first time a time sequence of the penumbral spectra. These penumbral spectra enable us to study the centre-to-limb variations of solar Fraunhofer lines when the Earth is transiting Sun. The Na i and Ca ii absorption features reported from previous lunar eclipse observations are demonstrated to be CLV features, which dominate the corresponding line profiles and mask possible planetary signal. Detecting atmospheric species in exoplanets via transit spectroscopy must account for the CLV effect.Comment: 9 pages, 11 figures, accepted, A&

    The effect of the stellar absorption line centre-to-limb variation on exoplanet transmission spectrum observations

    Full text link
    Transit spectroscopy is one of the most commonly used techniques for exoplanet atmosphere characterisation. This technique has been used to detect ionized and neutral species in exoplanet atmospheres by comparing the observed stellar lines in and out of transit. The centre-to-limb variation (CLV) of the stellar lines across the stellar disk is an important effect for transmission spectroscopy, since it results in a change of stellar line depth when the planet transits different parts of the stellar disk. We reanalyse the transit data of HD 189733b taken with the HARPS spectrograph to study the CLV effect during transit. The transmission light curve of the Na i D line so obtained shows a clear imprint of the CLV effect. We use a one-dimensional non-LTE stellar spectral model to simulate the CLV effect. After applying the correction, the measurement of the Na i absorption in the atmosphere of HD 189733b becomes better determined. We compare the CLV effect of HD 189733b to that of HD 209458b. The CLV effects are different for these two benchmark planetary systems and this is attributed to their different stellar effective temperatures and transit impact parameters. We then explore the general CLV effect that occurs during exoplanet transits. Normally, a star with a lower effective temperature exhibits a stronger CLV effect and its CLV feature extends over a relatively broad wavelength range. The transit impact parameter (b) describes the transit trajectory on the stellar disk and thus determines the actual manifestation of the CLV effect. We introduce a b-diagram which describes the behavior of the CLV effect as the function of different impact parameters. With improving observational precision, a careful modeling and correction of the CLV effect is necessary for exoplanet atmosphere characterisation using transit spectroscopy.Comment: Accepted for publishing on A&

    Plasma Surface Treatment of Powder Materials — Process and Application

    Get PDF
    Polyolefin particles are hydrophobic, and this prevents their use for various applications. Plasma treatment is an environment-friendly polyolefin hydrophilisation method. We developed an industrial-scale plant for plasma treatment of particles as small as micrometers in diameter. Materials such as PE waxes, UHMWPE and powders for rotomolding production were tested to verify their new surface properties. We achieved significantly increased wettability of the particles, so that they are very easily dispersive in water without agglomeration, and their higher surface energy is retained even after sintering in the case of rotomolding powders

    Partial pressures of CO2 in epikarstic zone deduced from hydrogeochemistry of permanent drips, the Moravian Karst, Czech Republic

    Get PDF
    Permanent drips from straw stalactites of selected caves of the Moravian Karst were studied during one-year period. A hypothetical partial pressure of CO2 that has participated in limestone dissolution, PCO2(H)=10-1.53±0.04, was calculated from the dripwater chemistry. The value significantly exceeds the partial pressures generally measured in relevant shallow karst soils, PCO2(soil)=10-2.72±0.02. This finding may have important implications for karst/cave conservation and paleoenvironmental reconstructions.Keywords: cave, carbon dioxide, dripwater, hydrogeochemistry,hypothetical partial pressure, karst processes, karstification model

    Plasma Surface Treatment of Powder Materials — Process and Application

    Get PDF
    Polyolefin particles are hydrophobic, and this prevents their use for various applications. Plasma treatment is an environment-friendly polyolefin hydrophilisation method. We developed an industrial-scale plant for plasma treatment of particles as small as micrometers in diameter. Materials such as PE waxes, UHMWPE and powders for rotomolding production were tested to verify their new surface properties. We achieved significantly increased wettability of the particles, so that they are very easily dispersive in water without agglomeration, and their higher surface energy is retained even after sintering in the case of rotomolding powders
    corecore