250 research outputs found

    Valency of rare earths in RIn3 and RSn3: Ab initio analysis of electric-field gradients

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    In RIn3 and RSn3 the rare earth (R) is trivalent, except for Eu and Yb, which are divalent. This was experimentally determined in 1977 by perturbed angular correlation measurements of the electric-field gradient on a 111Cd impurity. At that time, the data were interpreted using a point charge model, which is now known to be unphysical and unreliable. This makes the valency determination potentially questionable. We revisit these data, and analyze them using ab initio calculations of the electric-field gradient. From these calculations, the physical mechanism that is responsible for the influence of the valency on the electric-field gradient is derived. A generally applicable scheme to interpret electric-field gradients is used, which in a transparent way correlates the size of the field gradient with chemical properties of the system.Comment: 10 page

    Sound and Heat Absorption by a 2D Electron Gas in an Odd-Integer Quantized-Hall Regime

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    The absorption of bulk acoustic phonons in a two-dimensional (2D) GaAs/AlGaAs heterostructure is studied (in the clean limit) where the 2D electron-gas (2DEG), being in an odd-integer quantum-Hall state, is in fact a spin dielectric. Of the two channels of phonon absorption associated with excitation of spin waves, one, which is due to the spin-orbit (SO) coupling of electrons, involves a change of the spin state of the system and the other does not. We show that the phonon-absorption rate corresponding to the former channel (in the paper designated as the second absorption channel) is finite at zero temperature (TT), whereas that corresponding to the latter (designated as the first channel) vanishes for T→0T\to 0. The long-wavelength limit, being the special case of the first absorption channel, corresponds to sound (bulk and surface) attenuation by the 2DEG. At the same time, the ballistic phonon propagation and heat absorption are determined by both channels. The 2DEG overheat and the attendant spin-state change are found under the conditions of permanent nonequilibrium phonon pumping.Comment: 26 pages, 2 figure

    Nitrogen forms affect root structure and water uptake in the hybrid poplar

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    The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake)

    Careers in context: An international study of career goals as mesostructure between societies' career-related human potential and proactive career behaviour

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    Careers exist in a societal context that offers both constraints and opportunities for career actors. Whereas most studies focus on proximal individual and/or organisational-level variables, we provide insights into how career goals and behaviours are understood and embedded in the more distal societal context. More specifically, we operationalise societal context using the career-related human potential composite and aim to understand if and why career goals and behaviours vary between countries. Drawing on a model of career structuration and using multilevel mediation modelling, we draw on a survey of 17,986 employees from 27 countries, covering nine of GLOBE's 10 cultural clusters, and national statistical data to examine the relationship between societal context (macrostructure building the career-opportunity structure) and actors' career goals (career mesostructure) and career behaviour (actions). We show that societal context in terms of societies' career-related human potential composite is negatively associated with the importance given to financial achievements as a specific career mesostructure in a society that is positively related to individuals' proactive career behaviour. Our career mesostructure fully mediates the relationship between societal context and individuals' proactive career behaviour. In this way, we expand career theory's scope beyond occupation- and organisation-related factors

    Career mobility in a global era: advances in managing expatriation and repatriation

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    The surge of interest in expatriation and repatriation within the broader discourse on labor mobility of professionals and high-skilled labor, human capital development and the theory and practice of people management, serves as the backdrop to this paper. We propose that expatriation and repatriation be framed in the context of global careers and embedded in the wider social-economic environment of globalization through the lens of a career ecosystem theory. We chart the evolution of scholarly publications on career mobility over the past four decades and highlight current trends, in particular the emergence of self-initiated expatriation as a pivotal change in the direction of expatriation studies and derived practice. We assess the rigor of empirical findings, weigh theoretical underpinnings, offer a research agenda for future research and outline managerial implications

    Careers of highly educated self-initiated expatriates : observations from studies among Finnish business professionals

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    This chapter reviews existing literature about the careers of self-initiated expatriates and analyzes the different studies carried out among university level educated Finnish business professionals. A series of studies carried out among members of the Finnish Association of Business School Graduates during the last 15 years was cross-analyzed. The studies are based on three surveys and further interviews among their expatriate members (1999, 2004 and a follow-up study in 2012) also involving SIEs. Therefore, this chapter provide an overview of what we know about the careers of Finnish SIEs and show evidence of (1) their career motives, (2) the role of family considerations in the career decision making of SIEs, (3) the development of career capital and social capital during SIE-experiences, and also (4) longer-term career impacts of SIE-experiences. Based on the literature review and analysis of above mentioned studies we highlight the gaps in in the knowledge about SIEs and suggest areas where further research is needed.fi=vertaisarvioitu|en=peerReviewed

    Embryonic Diapause Is Conserved across Mammals

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    Embryonic diapause (ED) is a temporary arrest of embryo development and is characterized by delayed implantation in the uterus. ED occurs in blastocysts of less than 2% of mammalian species, including the mouse (Mus musculus). If ED were an evolutionarily conserved phenomenon, then it should be inducible in blastocysts of normally non-diapausing mammals, such as domestic species. To prove this hypothesis, we examined whether blastocysts from domestic sheep (Ovis aries) could enter into diapause following their transfer into mouse uteri in which diapause conditions were induced. Sheep blastocysts entered into diapause, as demonstrated by growth arrest, viability maintenance and their ED-specific pattern of gene expression. Seven days after transfer, diapausing ovine blastocysts were able to resume growth in vitro and, after transfer to surrogate ewe recipients, to develop into normal lambs. The finding that non-diapausing ovine embryos can enter into diapause implies that this phenomenon is phylogenetically conserved and not secondarily acquired by embryos of diapausing species. Our study questions the current model of independent evolution of ED in different mammalian orders
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