537 research outputs found
The order of the quantum chromodynamics transition predicted by the standard model of particle physics
We determine the nature of the QCD transition using lattice calculations for
physical quark masses. Susceptibilities are extrapolated to vanishing lattice
spacing for three physical volumes, the smallest and largest of which differ by
a factor of five. This ensures that a true transition should result in a
dramatic increase of the susceptibilities.No such behaviour is observed: our
finite-size scaling analysis shows that the finite-temperature QCD transition
in the hot early Universe was not a real phase transition, but an analytic
crossover (involving a rapid change, as opposed to a jump, as the temperature
varied). As such, it will be difficult to find experimental evidence of this
transition from astronomical observations.Comment: 7 pages, 4 figure
How Do Galaxies Get Their Gas?
Not the way one might have thought. In hydrodynamic simulations of galaxy
formation, some gas follows the traditionally envisioned route, shock heating
to the halo virial temperature before cooling to the much lower temperature of
the neutral ISM. But most gas enters galaxies without ever heating close to the
virial temperature, gaining thermal energy from weak shocks and adiabatic
compression, and radiating it just as quickly. This ``cold mode'' accretion is
channeled along filaments, while the conventional, ``hot mode'' accretion is
quasi-spherical. Cold mode accretion dominates high redshift growth by a
substantial factor, while at z<1 the overall accretion rate declines and hot
mode accretion has greater relative importance. The decline of the cosmic star
formation rate at low z is driven largely by geometry, as the typical cross
section of filaments begins to exceed that of the galaxies at their
intersections.Comment: 7 pages, 1 figure. To be published in the proceedings of the
IGM/Galaxy Connection- The Distribution of Baryons at z=0 conferenc
nIFTY galaxy cluster simulations - III. The similarity and diversity of galaxies and subhaloes
We examine subhaloes and galaxies residing in a simulated cold dark matter galaxy cluster ( = 1.1 × 10 M) produced by hydrodynamical codes ranging from classic smooth particle hydrodynamics (SPH), newer SPH codes, adaptive and moving mesh codes. These codes use subgrid models to capture galaxy formation physics. We compare how well these codes reproduce the same subhaloes/galaxies in gravity-only, non-radiative hydrodynamics and runs by looking at the overall subhalo/galaxy distribution and on an individual object basis. We find that the subhalo population is reproduced to within 10 per cent for both dark matter only and non-radiative runs, with individual objects showing code-to-code scatter of 0.1 dex, although the gas in non-radiative simulations shows significant scatter. Including feedback physics significantly increases the diversity. Subhalo mass and distributions vary by ≈20 per cent. The galaxy populations also show striking code-to-code variations. Although the Tully–Fisher relation is similar in almost all codes, the number of galaxies with 10 M 10 M can differ by a factor of 4. Individual galaxies show code-to-code scatter of ~0.5 dex in stellar mass. Moreover, systematic differences exist, with some codes producing galaxies 70 per cent smaller than others. The diversity partially arises from the inclusion/absence of active galactic nucleus feedback. Our results combined with our companion papers demonstrate that subgrid physics is not just subject to fine-tuning, but the complexity of building galaxies remains a challenge. We argue that even basic galaxy properties, such as stellar mass to halo mass, should be treated with errors bars of ~0.2–0.4 dex
Sagittal realignment osteotomy for increased posterior tibial slope after opening-wedge high tibial osteotomy: a case report
A 40 year old welder who underwent opening-wedge high tibial osteotomy for correction of alignment in a varus knee developed persistent pain with loss of knee extension. The posterior tibial slope increased from 9 degrees to 20 degrees after the osteotomy and caused the anteromedial knee pain and limited extension. The patient then underwent a revision osteotomy using a closing wedge technique to correct tibial slope. The osteotomy was performed, first from the medial cortex in the lateral direction, and second in the anteroposterior direction to remove the tibial bone in wedge shape and obtain full extension of the knee. The posterior tibial slope decreased to 8 degrees after the revision osteotomy and the patients returned to pain-free daily life. We reviewed this unique technique for correction of sagittal malalignment using a closing-wedge osteotomy for revision after opening-wedge osteotomy
nIFTY galaxy cluster simulations - III. The similarity and diversity of galaxies and subhaloes
We examine subhaloes and galaxies residing in a simulated cold dark matter galaxy cluster ( = 1.1 × 10 M) produced by hydrodynamical codes ranging from classic smooth particle hydrodynamics (SPH), newer SPH codes, adaptive and moving mesh codes. These codes use subgrid models to capture galaxy formation physics. We compare how well these codes reproduce the same subhaloes/galaxies in gravity-only, non-radiative hydrodynamics and runs by looking at the overall subhalo/galaxy distribution and on an individual object basis. We find that the subhalo population is reproduced to within 10 per cent for both dark matter only and non-radiative runs, with individual objects showing code-to-code scatter of 0.1 dex, although the gas in non-radiative simulations shows significant scatter. Including feedback physics significantly increases the diversity. Subhalo mass and distributions vary by ≈20 per cent. The galaxy populations also show striking code-to-code variations. Although the Tully–Fisher relation is similar in almost all codes, the number of galaxies with 10 M 10 M can differ by a factor of 4. Individual galaxies show code-to-code scatter of ~0.5 dex in stellar mass. Moreover, systematic differences exist, with some codes producing galaxies 70 per cent smaller than others. The diversity partially arises from the inclusion/absence of active galactic nucleus feedback. Our results combined with our companion papers demonstrate that subgrid physics is not just subject to fine-tuning, but the complexity of building galaxies remains a challenge. We argue that even basic galaxy properties, such as stellar mass to halo mass, should be treated with errors bars of ~0.2–0.4 dex
nIFTy galaxy cluster simulations – V. Investigation of the cluster infall region
We examine the properties of the galaxies and dark matter haloes residing in the cluster infall region surrounding the simulated cold dark matter galaxy cluster studied by Elahi et al. at = 0. The 1.1 × 10 M galaxy cluster has been simulated with eight different hydrodynamical codes containing a variety of hydrodynamic solvers and sub-grid schemes. All models completed a dark-matter-only, non-radiative and full-physics run from the same initial conditions. The simulations contain dark matter and gas with mass resolution = 9.01 × 10 M and = 1.9 × 10 M, respectively. We find that the synthetic cluster is surrounded by clear filamentary structures that contain ~60 per cent of haloes in the infall region with mass ~10–10 M, including 2–3 group-sized haloes (>10 M). However, we find that only ~10 per cent of objects in the infall region are sub-haloes residing in haloes, which may suggest that there is not much ongoing pre-processing occurring in the infall region at = 0. By examining the baryonic content contained within the haloes, we also show that the code-to-code scatter in stellar fraction across all halo masses is typically ~2 orders of magnitude between the two most extreme cases, and this is predominantly due to the differences in sub-grid schemes and calibration procedures that each model uses. Models that do not include active galactic nucleus feedback typically produce too high stellar fractions compared to observations by at least ~1 order of magnitude.The authors would like the acknowledge the Centre for High Performance Computing in Rosebank, Cape Town, for financial support and for hosting the ‘Comparison Cape Town’ workshop in 2016, July. The authors would further like to acknowledge the support of the International Centre for Radio Astronomy Research (ICRAR) node at the University of Western Australia (UWA) in hosting the precursor workshop ‘Perth Simulated Cluster Comparison’ in 2015, March; the financial support of the UWA Research Collaboration Award 2014 and 2015 schemes; the financial support of the ARC Centre of Excellence for All Sky Astrophysics (CAASTRO) CE110001020 and ARC Discovery Projects DP130100117 and DP140100198. We would also like to thank the Instituto de Fisica Teorica (IFT-UAM/CSIC in Madrid) for its support, via the Centro de Excelencia Severo Ochoa Program under Grant No. SEV- 2012-0249, during the three-week workshop ‘nIFTy Cosmology’ in 2014, where the foundation for the whole comparison project was established.
JA acknowledges support from a post-graduate award from STFC. PJE is supported by the SSimPL programme and the Sydney Institute for Astronomy (SIfA) and Australian Research Council (ARC) grants DP130100117 and DP140100198. AK is supported by the Ministerio de Econom´ıa y Competitividad (MINECO) in Spain through grant AYA2012-31101 as well as the ConsoliderIngenio 2010 Programme of the Spanish Ministerio de Ciencia e Innovacion (MICINN) under grant MultiDark CSD2009-00064. ´ He also acknowledges support from the ARC grant DP140100198. He further thanks Noonday Underground for surface noise. STK acknowledges support from STFC through grant ST/L000768/1. CP acknowledges the support of the ARC through Future Fellowship FT130100041 and Discovery Project DP140100198. WC and CP acknowledge the support of ARC DP130100117. GY and FS acknowledge support from MINECO (Spain) through the grant AYA 2012-31101. GY thanks also the Red Espanola de Supercomputa- ˜ cion for granting the computing time in the Marenostrum Supercomputer at BSC, where all the MUSIC simulations have been performed. AMB is supported by the DFG Research Unit 1254 ‘Magnetisation of interstellar and intergalactic media’ and by the DFG Cluster of Excellence ‘Universe’. GM acknowledge support from the PRIN-MIUR 2012 Grant ‘The Evolution of Cosmic Baryons’ funded by the Italian Minister of University and Research, by the PRIN-INAF 2012 Grant ‘Multi-scale Simulations of Cosmic Structures’, by the INFN INDARK Grant and by the ‘Consorzio per la Fisica di Trieste’. IGM acknowledges support from an STFC Advanced Fellowship. EP acknowledges support by the ERC grant ‘The Emergence of Structure During the Epoch of Reionization’
High apex predator biomass on remote Pacific islands
Author Posting. © The Author(s), 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Coral Reefs 26 (2007): 47-51, doi:10.1007/s00338-006-0158-x.On coral reefs in Palmyra—a central Pacific atoll with limited fishing
pressure—total fish biomass is 428 and 299% greater than on reefs in nearby
Christmas and Fanning Islands. Large apex predators –groupers, sharks, snappers, and
jacks larger than 50 cm in length- account for 56% of total fish biomass in Palmyra on
average, but only 7% and 3% on Christmas and Fanning. These biomass proportions
are remarkably similar to those previously reported for the remote and uninhabited
Northwest Hawaiian Islands (NWHI) and densely populated Main Hawaiian Islands
(MHI), although Palmyra’s reefs are dominated in biomass by sharks (44% of the
total), whereas the NWHI by jacks (39%). Herbivorous fish biomass was also greater
on Palmyra than on Christmas and Fanning (343% and 207%, respectively). These
results and previous findings indicate that remote, uninhabited islands support high
levels of consumers, and highlight the importance of healthy coral reef ecosystems as
reference points for assessment of human impacts and establishment of restoration
goals
Entrepreneurs’ age, institutions, and social value creation goals: a multi-country study
This study explores the relationship between an entrepreneur's age and his/her social value creation goals. Building on the lifespan developmental psychology literature and institutional theory, we hypothesize a U-shaped relationship between entrepreneurs’ age and their choice to create social value through their ventures, such that younger and older entrepreneurs create more social value with their businesses while middle age entrepreneurs are relatively more economically and less socially oriented with their ventures. We further hypothesize that the quality of a country’s formal institutions in terms of economic, social, and political freedom steepen the U-shaped relationship between entrepreneurs’ age and their choice to pursue social value creation as supportive institutional environments allow entrepreneurs to follow their age-based preferences. We confirm our predictions using multilevel mixed-effects linear regressions on a sample of over 15,000 entrepreneurs (aged between 18 and 64 years) in 45 countries from Global Entrepreneurship Monitor data. The findings are robust to several alternative specifications. Based on our findings, we discuss implications for theory and practice, and we propose future research directions
nIFTy galaxy cluster simulations II: radiative models
We have simulated the formation of a massive galaxy cluster (M = 1.110) in a CDM universe using 10 different codes (RAMSES, 2 incarnations of AREPO and 7 of GADGET), modeling hydrodynamics with full radiative subgrid physics. These codes include Smoothed-Particle Hydrodynamics (SPH), spanning traditional and advanced SPH schemes, adaptive mesh and moving mesh codes. Our goal is to study the consistency between simulated clusters modeled with different radiative physical implementations - such as cooling, star formation and AGN feedback. We compare images of the cluster at , global properties such as mass, and radial profiles of various dynamical and thermodynamical quantities. We find that, with respect to non-radiative simulations, dark matter is more centrally concentrated, the extent not simply depending on the presence/absence of AGN feedback. The scatter in global quantities is substantially higher than for non-radiative runs. Intriguingly, adding radiative physics seems to have washed away the marked code-based differences present in the entropy profile seen for non-radiative simulations in Sembolini et al. (2015): radiative physics + classic SPH can produce entropy cores. Furthermore, the inclusion/absence of AGN feedback is not the dividing line -as in the case of describing the stellar content- for whether a code produces an unrealistic temperature inversion and a falling central entropy profile. However, AGN feedback does strongly affect the overall stellar distribution, limiting the effect of overcooling and reducing sensibly the stellar fraction
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