1,494 research outputs found
Venting of fission products and shielding in thermionic nuclear reactor systems
Most thermionic reactors are designed to allow the fission gases to escape out of the emitter. A scheme to allow the fission gases to escape is proposed. Because of the low activity of the fission products, this method should pose no radiation hazards
Kinematic Constraints on Formation of Bound States of Cosmic Strings - Field Theoretical Approach
Superstring theory predicts the potential formation of string networks with
bound states ending in junctions. Kinematic constraints for junction formation
have been derived within the Nambu-Goto thin string approximation. Here we test
these constraints numerically in the framework of the Abelian-Higgs model in
the Type-I regime and report on good agreement with the analytical predictions.
We also demonstrate that strings can effectively pass through each other when
they meet at speeds slightly above the critical velocity permitting bound state
formation. This is due to reconnection effects that are beyond the scope of the
Nambu-Goto approximation.Comment: 6 pages, 12 eps figures - matches the published versio
Cosmic Strings and Superstrings
Cosmic strings are predicted by many field-theory models, and may have been
formed at a symmetry-breaking transition early in the history of the universe,
such as that associated with grand unification. They could have important
cosmological effects. Scenarios suggested by fundamental string theory or
M-theory, in particular the popular idea of brane inflation, also strongly
suggest the appearance of similar structures. Here we review the reasons for
postulating the existence of cosmic strings or superstrings, the various
possible ways in which they might be detected observationally, and the special
features that might discriminate between ordinary cosmic strings and
superstrings.Comment: Minor errors corrected and some references added, 34 pages, 6 figure
Perfectionism and achievement goals in young Finnish ice-hockey players aspiring to make the Under-16 national team
Research on perfectionism suggests that is it useful to differentiate between perfectionistic strivings and perfectionistic concerns. Regarding the 2 x 2 achievement goal framework, the usefulness of this differentiation was recently demonstrated in a study with university student athletes (Stoeber, Stoll, Pescheck, & Otto, 2008, Study 2), in which it was found that perfectionistic strivings were associated with mastery-approach and performance-approach goals and perfectionistic concerns with mastery-avoidance, performance-approach, and performance-avoidance goals. Because the study was largely exploratory and only used non-elite athletes, the aim of the present research was to replicate and extend these findings by investigating a sample of 138 young, elite ice-hockey players, while adding further measures of perfectionism and using structural equation modelling (SEM) to confirm the relationships between perfectionistic strivings, perfectionistic concerns,and the 2 x 2 achievement goals. The SEM results showed that, in elite athletes also, perfectionistic strivings are associated with mastery-approach and performance-approach goals, whereas perfectionistic concerns are associated with masteryavoidance,
performance-approach, and performance-avoidance goals. Our findings corroborate the importance of differentiating between perfectionistic strivings and perfectionistic concerns when studying perfectionism in sports, because
only perfectionistic concerns (and not perfectionistic strivings) are associated with maladaptive patterns of achievement goals
Elliptical Galaxies and Bulges of Disk Galaxies: Summary of Progress and Outstanding Issues
This is the summary chapter of a review book on galaxy bulges. Bulge
properties and formation histories are more varied than those of ellipticals. I
emphasize two advances: 1 - "Classical bulges" are observationally
indistinguishable from ellipticals, and like them, are thought to form by major
galaxy mergers. "Disky pseudobulges" are diskier and more actively star-forming
(except in S0s) than are ellipticals. Theys are products of the slow
("secular") evolution of galaxy disks: bars and other nonaxisymmetries move
disk gas toward the center, where it starbursts and builds relatively flat,
rapidly rotating components. This secular evolution is a new area of galaxy
evolution work that complements hierarchical clustering. 2 - Disks of
high-redshift galaxies are unstable to the formation of mass clumps that sink
to the center and merge - an alternative channel for the formation of classical
bulges. I review successes and unsolved problems in the formation of
bulges+ellipticals and their coevolution (or not) with supermassive black
holes. I present an observer's perspective on simulations of dark matter galaxy
formation including baryons. I review how our picture of the quenching of star
formation is becoming general and secure at redshifts z < 1. The biggest
challenge is to produce realistic bulges+ellipticals and disks that overlap
over a factor of 10**3 in mass but that differ from each other as observed over
that whole range. Second, how does hierarchical clustering make so many giant,
bulgeless galaxies in field but not cluster environments? I argue that we rely
too much on AGN and star-formation feedback to solve these challenges.Comment: 46 pages, 10 postscript figures, accepted for publication in Galactic
Bulges, ed. E. Laurikainen, R. F. Peletier, & D. A. Gadotti (New York:
Springer), in press (2015
GOODS-Herschel: star formation, dust attenuation, and the FIR-radio correlation on the main sequence of star-forming galaxies up to z=4
We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z sime 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rateâM* correlation is consistent with being constant sime0.8 up to z sime 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIRâradio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z sime 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5â4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z sime 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z â„ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts
What Counts as âWorld Classâ? : Global University Rankings and Shifts in Institutional Strategies
Global university rankings have emerged as a benchmark of institutional success, setting standards for higher education policymaking and institutional practices. Nevertheless, only a marginal share of higher education institutions (HEI) are in a realistic position to be ranked as a âworld-classâ institutions. In the European context, the global rankings have been used to highlight a performance gap between European and North American institutions. Here the focus has been on the HEIs in the top-100 positions, causing concerns over European higher education. This has also become a marker of world-class university. We analyze the strategies of 27 Northern European universities in different tiers to learn how they have adjusted to the reality of ranking. We conclude that the references to global rankings have increased between 2014 and 2018. At the same time, the references to rankings have become more implicit in nature. Nevertheless, we find that the discourse of global comparison and excellence has become more common in the strategies. There are also emerging references to the regional role of universities, which are apparent in the strategies of universities that are clearly outside the top-100 ranked institutions. However, this is also a reflection of the discourse of world-class university.Peer reviewe
Pre-asthma : a useful concept for prevention and disease-modification? A EUFOREA paper. Part 1âallergic asthma
Funding The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.Peer reviewedPublisher PD
Determination of the b quark mass at the M_Z scale with the DELPHI detector at LEP
An experimental study of the normalized three-jet rate of b quark events with
respect to light quarks events (light= \ell \equiv u,d,s) has been performed
using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by
the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are
found to agree with theoretical predictions treating mass corrections at
next-to-leading order. Measurements of the b quark mass have also been
performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data
are found to be better described when using the running mass. The measurement
yields: m_b(M_Z) = 2.85 +/- 0.18 (stat) +/- 0.13 (exp) +/- 0.19 (had) +/- 0.12
(theo) GeV/c^2 for the CAMBRIDGE algorithm. This result is the most precise
measurement of the b mass derived from a high energy process. When compared to
other b mass determinations by experiments at lower energy scales, this value
agrees with the prediction of Quantum Chromodynamics for the energy evolution
of the running mass. The mass measurement is equivalent to a test of the
flavour independence of the strong coupling constant with an accuracy of 7
permil.Comment: 24 pages, 10 figures, Accepted by Eur. Phys. J.
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